It wasn't his arrogance, nor his stupidity the reason why he didn't use his bankai against Aizen. He knew what he was doing at that time. If he released his bankai at that point, he would pretty much destroy the large portion of the Earth because of the massive temperature.
He used his bankai against Juha Bach because he was in Seireitei at that point, and that world is much more durable than world of the living.
This battle takes place in Hidden Cloud Village so if old man Yama is in character (OP did stated that morals are on) than he will not release his bankai. That is my opinion...
Furthermore, I don't think Yama can beat Mihawk without using his bankai. Maybe, if he opens a senkaimon to drag Mihawk to a better place for a fight, but that would be out of character.
@bigz007: despite how much seiritei might be tougher than the real world, I honestly think it's more of Kubo's trolling and his failure to understand his own story -.- lol the temperatures should have destroyed at least the portions he was near, instead it only did it when he slashed, which would have made sense to use against aizen in one quick attack or if aizen was stupid enough to try and stab him himself. but like i said, it's really kubos fault in the end XD
Just like when Aizen said he knew about Ichigo and his powers since the moment he was born. Everyone was thinking Kubo is trolling with that one, but later on he explained why Aizen said that.
It's the same with this, I don't think everything should be explained right away. Kubo can still make it happen.
It wasn't his arrogance, nor his stupidity the reason why he didn't use his bankai against Aizen. He knew what he was doing at that time. If he released his bankai at that point, he would pretty much destroy the large portion of the Earth because of
Weren't they in some sort of "alternative" Earth made by Urahara?
I remember it vaguely