This is major spoilers for later on in tybw . I had come up with this conclusion and is like it all makes sense. Kubo prob didn't even know aizen did this

Basically when aizen first fought yubahaha his main goal was not to fight yubahaha at all but to test if kyoka suigetsu could manipulate the almighty. You remember when aizen said "ah so you appesr to think am ichigo" that basically confirms it because aizen would know that it would be futile to do something like this to create an opportunity for ichigo or renji to win because if that was rhe goal it would've led to nothing. Aizen has already applied his kyoka suigetsu on the almighty from the very start and that fight was just to test it. Because if the almighty saw through that he wouldn't have been surprised that it was Aizen. Aizen said that you appear to think i am ichigo because yubahaha confirm for aizen that he hadn't forseen this, due to aizen having manipulated his almighty. Aizen was smiling when stabbed cus now he can just use that to trick Yubahaha into picking a future which ichigo wins. Aizen perfect countered Yubahaha. Yubahaha would've not been possible as a villain cus he's too op if it weren't for Aizen🔥🔥🔥🔥 he truely is 701 iq