We have absolutely no clue how high Aizen's reiatsu actually plateaus. People are making him out to be some mook in comparison to Yamamoto and Unohana.
Aizen got fucked up by Ichigo because at the time, they were both transcendent. Easily the two most powerful beings shown thus far in the series. Their power was on another plane of existence.
Yamamoto wasn't so strong he made everything burn up just because he's that strong, it's because his sword was a fucking fire type.
Yes, Aizen admits that Yamamoto was stronger than him and he would lose in a straight fight with no illusions. People are making it out like these guys are gods that could have solved the whole conflict by themselves though, which is absolute nonsense.
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