Stranger Things being poorly written is not something you can debate on. It isn't open to interpretation how royally they fucked up their show. It frustrates me to my core when I see someone defending it because the problems it does have are so disgustingly blatant that you'd have to watch the show with your eyes closed and never interact with the fandom for the show to avoid it.
The bigotry written between the lines (and sometimes straight up into them) is so damning, but people seem to refuse to see it (I wonder who and I wonder why).
We can start with how the women are treated in the show.
El/Jane (whatever you'd like to call her) spent the entire show having her agency stripped from her time and time again. It was the lab, initially. Then enters Jim Hopper who, despite the efforts of the show to explain his controlling nature as just a natural over-protectiveness that comes from an out-of-practice father trying to protect his daughter, ends up coming across as overly angry and unnecessarily miscommunicating at every turn. Then enters her canonical boyfriend Mike who, despite being a child himself with not the best role models for healthy relationships, still often puts her in this position where she has to be something she simply doesn't want to be. A superhero.
At every turn, Eleven has her agency taken from her. Even with good intentions from the characters, it is a constant loop of her never getting what she truly wants, which is to be free of it all and have the ability to live a normal life. The way they resolve this plot? They have her kill herself. In the end, she just represented 'the magic of childhood', right? There couldn't have POSSIBLY been any other overarching themes in her story that deserved resolution, right? Right?
Nancy started off as a compelling character with a clear arc that worked in her favor. Former smalltown girl who turned the grief and guilt of losing her best friend into a drive to avenge her death and protect what was hers. But as each season goes on, it strays further and further away from that narrative for her and starts to reduce her to the tropes they put on her. Instead of being a complex female character with an emotional call-to-action, she becomes Girl With Gun and Girl In Love Triangle. Even the depth they TRY to add to her character in S5 falls flat because of how poorly written the dialogue is (not to mention her inexplicably shooting the oppressive force in the sky ultimately making things worse as if she's not supposed to be one of the smartest in the group.)
The same can be said for Joyce Byers, by the way!
Karen Wheeler upsets me to my core, because they took what was an amazing mother and put her in the middle of the most disgusting plot they could imagine. Regardless of what you think of Billy as a character, he was still 17 canonically when her fixation on him started. She was 43 years old. She knew how old he was too because she knew he was in her daughter's classes. She then ends up agreeing to having sexual relations with this boy after he's freshly 18, and the only reason she stopped was because of her marriage and kids, not his age.
And what's devastating is, prior to that plot and even beyond its 'resolution', she is shown to be a sweet, caring and thoughtful mother. To have introduced that in the middle of her story and moved on like nothing fucking happened is jarring. Karen Wheeler deserved to continue having a well-rounded arc uninterrupted by the Duffers poorly disguised fetish.
Moving on to how the characters of color are treated in the show.
Lucas has never had a full character arc that isn't related to white characters around him. In S1, he was a loyal member of the party and a minor antagonist to El/Jane. Everything after S2 is him basically being reduced to Max's Boyfriend. Even Dustin gets his own central plot, and the rest of the party members are so intensely vital to the main plot. Lucas not being offered the same is a very clear imbalance that no one talks about or pays attention to.
Erica is just reduced to the Sassy Black Woman trope and shows up for comic relief. The only thing I can think for something that makes her individual is her getting into D&D, but I don't really think that forgives the rest of her character and the role she's given in the story.
Argyle was also reduced to comic relief. However, he was set up to have a bigger role in the story at the end of S4, being shown in Hawkins. Jancy verbally alludes to him 'sticking around'. This culminated in nothing, as Eduardo Franco had to find out he wasn't being brought back through an official social media post.
By far the most egregious example of the racism (and misogyny) in the show's writing is Kali Prasad. She was brought in for one episode, abandoned for two seasons and only mentioned one or two times. She was then brought back in the final season. She was made to watch her only family be quartered and shot in front of her. She was taken by the very people who traumatized her in the first place, losing her hair and her identity as she's then used as a living blood bag to restart the experiments (the source of her trauma). She's suicidal and feels as though her very existence is dangerous. Her need for El/Jane to agree to her plan is not coming from a place of wanting her sister to die, it's from her visceral fear of anyone ever living through what she did again and her need to put an end to the torture. She then spends the entire season being called a bitch and being treated like a threat. She then dies quickly, without fanfare. There's never a moment where Hopper sees the same look in Kali's eyes that he saw in El/Jane's. There's never a moment where they redeem her to anyone in the show. And her sister is the only person allowed to cry for and mourn her. Think about that for two seconds and tell me you don't want to punch something.
Moving on to the queer characters of the show.
Robin and Vickie's relationship was set up throughout Season 4, Vickie being Robin's first girlfriend. Their overarching development happens in the gap between Seasons 4 and 5, and we get very little time with them throughout the show. Their arc abruptly ends in the epilogue of the series, with Robin alluding (and the Duffers later confirming) that they have broken up. There is no explanation for this, only a mere comment from Robin about doing away with "overbearing partners".
Not only is this wildly out of character for Robin to say, as she herself is someone who knows what its like to be called overbearing for being anxious and caring too much, but it also was not hinted at throughout the show that there were any problems within their relationship. The only scene where they even fight is when Vickie understandably believes Robin is addicted to drugs after she stole some from the hospital and began talking about monsters from alternate dimensions. This is quickly resolved when the truth is revealed to Vickie on short notice, so there was no need to harp on it any longer. It was an understandable jump to make, and it was cleared up less than a fifteen minutes later. The only other problems in their relationship were Robin always canceling their dates together, which also is resolved by Vickie discovering the Upside Down is real and that's why Robin had been gone, and that it was her trying to protect Vickie from getting involved.
It would've taken the same amount of effort to simply put Robin and Vickie in the background at Enzo's for the Joyce and Hopper proposal scene. It also would've been just as easy to leave it open-ended. If there had been more conflict between them in the season to suggest their relationship wasn't the fairytale they thought it would be, a vague breakup might be more understandable. However, with everything we were given of them in the final season, a breakup was the most unnecessary inclusion to their arc. It took more time to do it than to not.
Let's finally address the elephant in the room, which is Byler. From the start, Mike’s bond with Will is written with a level of intensity that goes beyond normal friendship, and something that is not paralleled with any of the other party members (bar the ones who are canonically in a romantic relationship.) Mike never gives up searching for him, recognizes him just by his breathing, and frequently centers his emotions around Will. In many ways, the story treats Will as Mike’s emotional core, even when Jane should've been in that position if Mileven was supposed to be the endgame couple. At times, Jane herself even functions narratively as a bridge between them, with Mike’s connection to her frequently framed through his desire to save Will. This is not only a disservice to Will and Mike's relationship, but also Jane.
Their story includes the well-known Cyrano trope, which describes a shy or underdog character (the Cyrano) who helps a handsome but less articulate love interest woo the object of their affections. This leads to the love interest eventually falling in love with the words or sentiments of the Cyrano. When this is inevitably realized by the love interest, they realize their true affections lie with the Cyrano, as they fell harder for the feelings expressed in the art than they ever could for who the Cyrano was trying to set them up with. The important part of the trope is that there is a reveal of the true holder of said feelings, which was never actually addressed in Stranger Things, leaving a broken trope that was implemented seemingly for no reason.
Will and Mike's relationship is also often paralleled by Robin's relationship to Vickie in Season 5, and many things in the advice Robin gives Will to look for to signal that there was reciprocal attraction were visibly shown occurring between Byler's dynamic in later scenes. A bump of an elbow, a brush of a knee, a shared look. All were not only displayed between them, but often highlighted by prolonged camera focus on those moments. There's never an explanation as to why those didn't amount to anything in actuality. There's never a moment where Robin goes "these gestures could mean nothing and please don't look too deeply into them." They even have a prolonged shot of Robin looking between Will and Mike thoughtfully after this conversation occurs, watching the way they interact together.
Will and Mike's dynamic and screentime is also often paralleled their older siblings relationship, especially with them both featuring an arc with the Wheeler sibling seemingly unable to say they loved their partner at the time. With Nancy in Season 2, she is shown been unable to say the words 'I love you' to Steve first when she is drunk at a party. Then, the day after the party in a conversation with Steve, she is still unable to say it while sober and being directly asked by Steve to say it if she really meant it. Instead of saying it, or even outright saying she doesn't, she avoids the question. Tells Steve he's being ridiculous for even suggesting it, then continues to be unable to say it.
In Season 4, when Mike is around the same age Nancy was at the time, he is shown in a nearly identical conflict. Jane calls him out for not ever saying he loved her in his letters to her. And again, when she is directly asking him to say it to her while she is standing in front of him to witness it, he can't conjure the words. He says the same things, that she's being ridiculous for insinuating he doesn't love her despite still not saying it. The only time Mike manages to say it is because Will encourages him to via the Cyrano trope, while she is unconscious, while Will is sitting directly next to him and verbally encouraging him to do so.
In Nancy's case, this was supposed to signal a sunsetting of her relationship to Steve. But in Mike's, it was supposedly just a moment of insecurity from him, despite not saying it once throughout the entirety of Season 5. An argument can be made that Mike not saying he loved Jane to her in her final moments was because he couldn't let go of her, and saying it would be like accepting it. An argument could be made that the moment wasn't about Mike or his feelings at all. But when placed next to all of the other tropes and parallels implemented into their story, it starts to become less of an intentional arc for their relationship and more a failing to act on the themes set up in the show. They could've had Mike say he loved Jane at any other point in the season as well, but that wasn't done either.
None of these parallels are ever expanded upon or actualized. Robin and Vickie's relationship is used to expand Will and Mike's, only for them to break up without reason or explanation. Will and Mike's relationship is then used to further Mike and Jane's relationship, only to be left unfulfilled in the end. And Mike and Jane's relationship is torn apart when Jane is killed off in the most unnecessary way. It's a never-ending loop, a snake that won't stop eating itself, and it goes on forever. And every single ship listed here suffers for it.
It literally isn't even just bad writing. To say the show is well written is to say that all of these things don't matter. These themes have a major impact on the minorities these characters represent, and to spit that back in our faces like we're crazy for being angry about it is bullshit.