I truly do not understand what Kubo's plan was...
I think Bleach was supposed to be a two Arc story, but (probably) a mix of Shonen Jump pressuring for more content and Kubo's own wish for fame and fortune (he's one of the rare ones that actually WANTS to be seen and adored as a public figure. ) made the (logical) absolute defeat of Aizen at the end of the Soul Society Arc impossible.
Now Kubo had no more original ideas.
Now Kubo needed to develop his work more... But he never truly had what was needed, which explains so, so many non-canon Arcs, Episodes and Movies that only have (rarely) his name somewhat attached.
The Arrancar Saga brings about the only good novelty (The Visored) and the Turn Back The Pendulum mini-arc.
Nel and her Gang is a mini-copy (parody of...) the Karakura Gang.
The Espada are an actual villainous copy paste of the moraly grey Shinigami (Grimmjow= Renji without the "redemption". Ulquiorra= Byakuya without any actual feelings, morals and redemption.)
Aizen has this very, very creepy interactions with Inoue first and Ichigo later on...
Inoue "She's One Of Us Now" supposedly has Godlike powers, but not really, because why are we suddenly trusting what the villains say?
Kenpachi is Kenpachi-ying, because Kubo is allergic to give that man an actual personality.
Mayuri is there because... Kubo created another horrible mad scientist for a face off, I guess?
Oh, and to make a portal for Ichigo because Urahara is never there from the get go...
Ichigo again as the quintessential Lamb To The Slaughter, because that's Kubo's kink (Ichigo learns nothing from the suffering each time since he keeps getting thrown into even worse messes, so there's no Character Growth actually. We see it because we project our own issues onto him.)
Isshin does nothing but berate his son, lie and, instead of sacrificing himself, readily offers his son's powers via Final Getsuga Tensho...
Ichigo wears Aizen out but his victory is stolen away by...ta-dah...Urahara!
Because in the end it didn't mean shit and all Urahara needed was to get some kido spell on Aizen... Who's now for some fucking reason technically immortal.
The Hogyoku should have had some "remnants" from when it was inside Rukia and "reject" Aizen altogether.
Villains CAN die. It's okay. Some deserve to...
Ichigo could have killed him and live happily with it.
Especially if TYBW didn't exist and Grand Fisher had been one other experiment of Kaname Tōsen (the actual scientist) sent by Aizen to Karakura.
Aizen would have been the causality (indirect killer) that brought about the actual cause (the one who did the killing) of Masaki's death...
Because for all of the boring parts of the Fullbringer Arc, (The Fullbringers are just villainous copy-paste of the Visored) I actually liked the final episodes and the (accidental?!?) message that the Karakura Team wasn't all that we were sold about.
There were no real, enduring friendships there.
And the ones who actually came to help (I have the theory that they were, in fact, forbidden from trying to contact Ichigo by Central 46. It makes sense. ) were the Shinigami.
But not just any Shinigami. The ones who had a connection to Ichigo...
And yes THIS should have been the end.
But then Kubo had his fingers in other "pies" that needed Bleach to churn out more characters... How else do you get to the 12th Anniversary of Bleach Brave Souls if you end your story?
How else do you get more revenue from the brand Soul Resonance game?
How do you keep KlubOutside relevant if no one wants to talk about Bleach anymore?
In the end, the likely answer for why Bleach is so convoluted and badly written is wanting to make money fast...
And for all that Kubo likes to come out and criticise Hellverse: The Movie, I don't see him turning away the revenue from the copywrited characters...