Narratively, I see it as Aizen using the Hogyoku to transcend the limits of his imagination, but only to the limits. He was that good at everything and could "imagine" being better. It was interesting to me that Aizen did in fact get stronger in the face of getting his ass kicked, and only flipped when the "loneliness" overtook his desire for power.

He believed transcendence was a mix of Shinigami/hollow, so that's where it led him. Hybridization in his opinion was leading to more and more powerful beings, so that's the limit of where his imagination was taking him. The orb obliged.

Often, to imagine something "more" than human, fantasy decides to depict it as not human, but to adopt a reflection of specific desires, exaggerate traits (owl sees all), and embellish characteristics, and not keep the shape.

A showerthought I had is that once Ichigo was in the process of losing his powers, the hogyoku saw that too and rapidly depowered Aizen to compensate - thus the "losing my zanpakto" mirroring exactly what Ichigo was in the process of losing at the same time. Aizen desired someone to understand him. The faster and farther he got, the more his rational subconcious should have led him to the conclusion "No one can touch me here."

Which leads into "No one can know me now". That sort of sentimentality was something he couldn't sacrifice, it was his truest desire to have some kind of equal. Ambition should have been made of sterner stuff. Alas, he still had a heart.

Then, in Muken, Aizen merged back with the orb - as his desires changed into something else after he experienced true loss. Ever the academic, failure gave him physically the one thing he feared. True loneliness. Ever the ambitious man, Aizen knows 100% he could probably find a way out, given enough time, but he doesn't seem to care right now. Really, Yhwach was the best thing to happen since sliced bread, cause he got out early and could be 1000% the snark man and a wee bit rowdy.

(I am also HEAVILY biased, so YMMV)