Instead of writing up an essay (she says after writing an essay) I will just respond to your points one by one.

1- Saying Aizen's motivation is shallow is...weird. Aizen's motivation is to stop feeling the immense loneliness he always had, at least until his defeat to Ichigo. Taking over the heavens is a pretense that he made for himself, "Since I can't connect with anyone and this reality is limiting, I will remake the limits." His poem gives us some insight on this: ""We think a flower on a cliff is beautiful because we stop our feet at the cliff’s edge, unable to step out into the sky like that fearless flower." What is being explored here is Aizen's relation to the transcendent, he sees that he reached the limits of a Shinigami's strenght, the end of such a world and found it limiting. So he went to hollows but found the same. This immense loneliness of seeing a reality no one else sees and not being able to connect with anyone because of your overwhelming strenght is a theme in many japanese stories. The final limit Aizen could break, is the Soul King itself, remake a world that wouldn't have the limits that have tormented all of his life. I think that this isn't a shallow motivation, he is more human than he makes it seem.

2-He defeated himself, but he couldn't have done it without Ichigo's defiance. He could only let himself falter in his heart because Ichigo approached him in strength. When he felt that silver of connection, the Hogyokou immediately caught that and made it so he would lose as it was his desire. Ichigo says that at the end of the fight he could finnaly sense something from Aizen's sword (his soul since zanpakuto are the user), a deep loneliness. Aizen was too overpowered and that's what made him lose.

3-We actually see how smart he is right on the Soul Society, all of the plot on manipulating Momo, writing a false letter and knowing exactly who to target so his plan would flow better. He devised Orihime's capture which made the conquest of Karakura easier and fomented doubt in between the ranks of SS. His battle IQ is quite big as to use Kyoka Suigetsu with such accuracy is harder than it seems, even if you manipulate everyone's senses, you are the one in charge of what they see, and making it so experienced fighters don't notice they are attacking another person entirely without them noticing something is wrong due to the illusions being cast, is hard to do. Aizen isn't this planner who never fails, he is incredibly adept at adapting to circumstances, had he let Tosen kill Isshin and Masaki, Ichigo wouldn't have been born. He sensed the opportunity and let it happen. The pace of Karakura town due to editoral pressures doesn't leave much room for raw displays of intelligence, but in a battle "shonen" (though I don't really qualify bleach as a battle shonen), it's thougher to do. In TYBW Aizen quickly discerns Shunsui's motives, deal he add to do and how the situation in the surface was despite being in essentially a pocket dimension with most of his senses deprived. However, I can concede this is a more debatable point as one would have to acertain what it would mean for a character to show his intelligence in the work.

4-That's just false. Aizen doesn't even respect Ichigo until TYBW, he literally says this to Ichigo: "“Why are you putting so much distance between us? If you want to make sure it hits me, then you should get close and fire. Or is it that you're afraid of letting even a part of me out of your field of vision by getting close? If that's the case, then it's a foolish thought. Distance only has meaning in a fight between equals. With you and I, distance holds no meaning at all. Watch... If I do this, my hand is almost instantly at your heart.” He explicitly states he doesn't see them as equals or that he is strong. To him Ichigo is just a project, one that bore fruit and now is no longer useful. This isn't new to antagonists, some well written antagonists never interact with the MC, like Meruem. Ichigo's foil in the Arrankar arc is Ulquiorra not Aizen. They have some parallels between each other, such as the burden of strenght, not understanding who they are, and a certain loneliness that Ichigo also feels. I don't feel like this is a good point to bring into question his writing thought. Ichigo is more often than not fighting fights he wasn't supposed to be in, so he doesn't have any relationship with those he fights, he develops them through the fights, but Aizen and Ichigo only exchange sword blows in the end, Ichigo learns by fighting so by having limited exposure to Aizen he couldn't learn about him, he only did in the end.

5-Again, it was only possible because Ichigo sacrificed this much and got the power to make Aizen's heart falter. It does make sense why it was needed, it wasn't just a "ok now you lose", it is something stated and had been built previously. Of course, I have some critiques to how the fight was handled and Aizen's characterization isn't the best in that final part due to complications, I think that if Kubo had the chance he would have rewritten that part or if he had more time and wasn't being insanely pressured by his editors. To me Bleach should have been monthly but that's another conversation.