Sometimes I wish I could draw because I start imagining fandom animatics in my head and I think I'd start sounding like a crazy person if I tried to explain the degree to which I plan them out in my head.
"Wow, you're yapping about Tidus and Jecht again. I think you have a problem." MAYBE I DO I DON'T KNOW, THEY MAKE ME SAD
This is a mix of me trying to figure out characterization and maybe random headcanons. Or you could call it yapping. That'd be more accurate.
The game already makes a point that Tidus did inherit some traits from Jecht, in some fashion. But I like to think, based off the Jecht sphere in Luca, that Tidus's crybaby-ness actually did come from Jecht. Maybe Tidus is a bit more overt with it, or maybe Jecht managed to suppress it growing up.
I think Tidus would probably avoid alcohol like the plague. Might irrationally think if a single drop passes his lips he's going to instantly become an alcoholic like his old man.
Take this with a grain of salt because I suck at visual-stuff (character designs and such), but I want to say that Tidus and Jecht share a lot of their design elements. They both have some sort of asymmetry with their legs (Tidus with the longer pant leg, Jecht with the sash), they both have the Zanarkand Abes logo on them (Tidus has the pendant, Jecht has the chest tattoo), they have more armor on one arm than the other, and I want to say their colors aren't the same but are kinda similar. In Dissidia I think their official art also kind of line up. But Tidus seems to have toned down versions of some of those same elements. He just has a pendant while Jecht has a big tattoo. Both his arms are covered while Jecht has a bare one against his armored one. I might try to throw together some image in Gimp so I don't sound completely crazy. Or maybe this is a very basic observation, I don't know.
I have zero canon basis for this but I like the image of the rare times Jecht had to look after baby!Tidus on his own, he'd hum the Hymn of the Fayth to try and get him to go sleep. Baby!Tidus didn't care that his dad's not a great singer.
As much as I like Tidus being upset about other people getting a "nice" Jecht for angst reasons... I think he probably is a little numb to it at this point. People back in Dream Zanarkand liked him enough to where they're holding a memorial cup for him. People talking about his dad and how great he was and hey aren't you finally going to do his shot? was probably pretty common for him. I think some of the NPCs at the very beginning of the game even do that. Although I think seeing people even in another world praise the man probably still is a little :/ if his initial reaction to Yuna bringing him up is anything.
Speaking of: I don't think it's that shocking that Yuna would say Jecht was a kind man. He was one of her father's guardians, she would be inclined to view him optimistically, and also Yuna's not his kid. Yeah he'll be nice to her, whatever, he's not invested in making sure she becomes a star player!
But admittedly before the end of the game, I don't think the knowledge of "Well, Jecht was bad to you, Tidus, because he loves you!" would be that comforting.
PROBABLY READING TOO MUCH INTO THINGS WARNING: When Jecht offers himself up to become a fayth, a big part of his reasoning is that he's realized he can't go back to his Zanarkand and see Tidus again, and there is some special emphasis placed on that part specifically. Which makes me wonder--if, for whatever reason, Jecht thought he could make it back to Dream Zanarkand... would he have joined Auron in fighting a little harder? Also something something it's probably just supposed to be a case of Tidus surpassing his dad (still fighting where Jecht just gave up) but this is the reading too much into things bullet points.
(You could also make a really dark joke about how, in a roundabout way, both of Tidus's parents committed suicide [even if I think Tidus's mom did probably die from an illness] because they were separated from someone they care about. And then his babysitter came to Spira off of a suicide run! Maybe that's why he's actually cool with sacrificing himself. Not any character reasons. It's just all the important adults in his life were not great role models for staying alive.)
SPECULATIVE TERRITORY: I guess it does lead a little credence to my idea that as much as Tidus's mom went into a downward spiral after Jecht's disappearance, if something horrible happened to Tidus Jecht would go into a mental spiral. I'm thinking mainly pre-ending up in Spira since, as Sin, Jecht probably had to come to terms with the fact that ending Yu Yevon was going to mean, at the very least, a temporary death for Tidus.
Like, if he got sick and died, or if he suddenly disappeared, or some other tragedy, Jecht would trudge along at first. What, no, he's fine. Life goes on. Drinks way more and way too much. Still insists he's fine, maybe even starts talking about how the stupid runt should have fought harder or stuck around, and nobody knows if that's just the grief talking. And then he spirals downward at maximum velocity.
Based off the flashback to when Jecht showed off the Jecht Shot to child!Tidus, I like to think that Tidus, if he did try blitzball stuff, would consciously do it away from his dad. And Jecht would just be annoyed and think "damn brat's trying to hide his practice from me!" And show up unannounced and oblivious as to why his kid would practice away from him.
BACK INTO SPECULATION TERRITORY, BUT ABOUT THEMES THIS TIME: I've had this idea in my head for a bit, based off Jecht wanting to make Tidus into a star player and show him the view from the top that Jecht may have always wanted Tidus to surpass him. By the time of the game proper it's more about Tidus killing him as Sin and putting an end to the spiral of death but I like to think even before that, he had this schmoopy fatherly idea that Tidus would become a better player than him. It got distorted and warped by his frankly bad parenting (to put it kindly) and probably the alcoholism too but it was there. I want to say I have some canon backing from the ~themes~ and how Spira's caught in stasis, and something something Buddhist themes of breaking cycles but I may be getting lost in the sauce there. I don't know I'd need to sit on the game a bit longer before trying to write a crazed analysis.
From a Doylist perspective the Sin-memory-weird-charade-conversation-with-father at Operation Mi'ihen being the one where Jecht goes "Nuh uh! I can stop being an alcoholic whenever! Why are you crying small child" is because it's not that far from the Moonflow and when Auron tells Tidus about Jecht quitting alcohol. But if I want to give it a more Watsonian explanation, it's either 1. Jecht reminding Tidus of a time Jecht was cruel to him to get him more inclined to kill Sin or 2. Jecht, maybe, in a very roundabout and emotionally stunted way, trying to apologize for the fact he didn't stop when Tidus told him to. Or maybe it's just casual Jecht memories Tidus got blasted with. Who knows. I guess this depends on how much control you think he has over what Tidus sees when he takes a ride on the Sin taxi.
Which. As bad as that memory makes him look to me in a more real-world context (dude, why does your 7-year-old know about your alcoholism?) I do think it's meaningful that in the corresponding Jecht sphere for the shoopuff incident that as much as Jecht mentions not inconveniencing Braska, his ending reasoning is that if he keeps screwing up (because of the alcoholism) his wife and Tidus would never forgive him.
Tidus's mom because wow she definitely is a character that shows up in... two scenes:
I think I agree with the sentiment that the flashbacks Tidus has of her at the farplane definitely make her look like not the best mom. But I don't know if I view her that negatively. I think for Tidus to be upset that she basically ditches him whenever Jecht's around, she probably has to be, worst case scenario, a decent mom when he's not in the picture.
And she didn't keel over until at least Auron had arrived in Zanarkand, so she didn't entirely leave Tidus by himself.
It's just that, if Jecht and Tidus were trapped in a burning building, and she could only absolutely save one or the other, no ifs ands or buts? She'd probably pick Jecht. It's not a good thing but it's a human thing. But that's speculating about a character that shows up in two scenes.
DIPPING INTO WILD HEADCANON TERRITORY: But admittedly I think that, if Jecht had tried to be more involved with raising Tidus beyond "neener neener I'm better at blitzball than you, small child" it'd probably become evident that if Tidus and Tidus's mom were trapped in a burning building, and he could only absolutely save one or the other, no ifs ands or buts, Jecht'd probably pick Tidus.
And if it was Tidus with the choice he would probably be "No! I'll find a way to save the both of them!" And in order to do that he would probably have to commit seppuku so uh. Maybe this family shouldn't be near burning buildings is the takeaway.