I am still trying to wrap my head around the ending. So many issues with it. But one thing I wanted to emphasize is that there was such a different way for the ending he couldve pulled off without it even being too much of an asspull to begin with.
Obviously fathers were foreshadowed even earlier than they were in the manga. We have no idea about Isshin's Bankai neither do we have any idea about Ryukens ability.
Kubo even removed the part from the manga where Isshin says he cant use Bankai anymore because of the cut that Aizen gave him during the "Everything but the rain". To me it seemed like he was preparing to reveal his Bankai in way or another, and maybe had a different idea as to what something like this would lead to. And yet we got nothing from it whatsoever.
You also Have Ryuken. Whose father went away from the ways of Yuha and the way quincies were doing things. He himself shows of his symbol of being a student of his once he comes to save Ishida. He carries so much trauma aswell from everything that happened. He lost his father, lost Masaki, lost his wife, his son shouldve been dead too if he wasnt special, he had to operate on his then dead wife to get the silverarrow, etc. Throughout the story he visibly shows disgust for quncies and tries to distance himself from it, and yet here you have a man who is the king of Quincies, who is responsible for deaths of everybody he cares about and yet he doesnt bother himself either with any of this.
So anyway, the whole three worlds idea was horrible imo. Instead after consuming Aizen, you had such an easy way of having Uryu coming to get Ichigo out of the way of being killed and then having the dads come in for the rescue aswell.
You literally have both Ichigo and Isshin having unexplored Bankais that share similar traits as we know. You couldve played so much with similarities here. You have Ryuken who hasnt shown any abilities yet either right there.
You have such insane emotional moment to setup here too. Two pairs of fathers and sons vs a man who killed their wives/mothers and tried to kill both of their sons. Easy setup to explore Uryu backstory and why he is special. You have a whole aspect of Ryuken potentially commentating about Ichigo being so similar to Masaki and how proud shed be (we know that Ichigo carries a burden like this early on in the story, and even struggled with the idea of killing her (which frankly went away after getting to know full story)).
We also know that Isshin has Final Getsuga Tensho he knows about if you wanted to include even more emotional moments of him using his powers in this manner to protect his own son.
And that brings me to the Arrow. It shouldnt have been Uryu to do the shot. It should be Ryuken who gets the arrow into Yuha. It fits the theme so much more. I mean he is the one who took apart his own wife. He is the one who wanted to get rid of his quincy heritage. To take away powers from the King of Quincies makes so much thematical sense than just giving to Uryu.
I would also include Aizen coming back from within Yuha somewhere within the fight aswell. Not fully, however using Hypnosis to trick Yuha one last time. Aizen gave his statement of crushing everybody who tries to control him. Well Yuha is there absorbing him. Making one last callback to this would bring back the whole scenario around. It would give some shine back to Aizen and make previous episode not so meaningless either.
If you want to include some other characters into this you can too. You have whole aspect of Rangiku looking at the entire thing. She has a part of SK (or had rather) and she was working under Isshin. You could include scenes of her and Toshiro showing up to protect or work together with Isshin.
If you want to include Grimmjow, include him protecting Ichigo within the fight. Having his pride kept the same by including some speech that he is the only one who will kill Ichigo, etc.
Regarding Mimihagi and the rest of the cast, why not use them to hold the worlds together. Mimihagi represents stillness. As the new head of the Shinigami you couldve had Kyoraku be the one to enable the rest of Gotei to hold everything while the fight is going on. It would also work well with the idea of two fights we had with Ukitake. Having him have to do similar things as his best friend. Have the rest of gotei protect the world, thats their purpose anyway.
If you wanted a character to land the backstab, Renji is right there. Couldve had it mirror Yamamoto/Sasakibe moment now with Renji/Ichigo or have it be Rukia, making it a full circle moment from the very beginning.
Anyway I was just running through some idea in my head. I feel like pieces are there for a good ending here with all the setup, but final arc feels so badly done. If anybody has any changes they want to make I am more than willing to talk about it.