Ichigo was on the ground about to be stabbed right before it went off. Even in that form, he STILL didn't actually beat the person he was facing.
I mean, no, he wasn't about to be stabbed. Aizen's zanpakuto literally crumbled away. And of course Ichigo didn't kill Aizen-- Aizen is absolutely immortal. Nothing can kill him.
And don't forget the next arc. Ichigo is just as beastly there as he is vs. Aizen. Still no berserk. He absolutely embarrassed Ginjo even after the guy stole a huge power boost from Ichigo. He only really goes berserk a couple of times in the series. His best showings (apart from the ulquiorra fight) are when he's calm and confident.
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I write Naruto Fanfiction. But I am definitely not a furry.