That might have been correct and acceptable if Ichigo didn't literally self-destruct by clinging to that assumption. Or if Aizen was gradually getting stronger and Ichigo was in a pinch he wouldn't get out without going into Chiaotzu mode. It would have been a good time to make Ichigo use it when Aizen got at or above his level and Ichigo needed to kill Zangetsu for a huge power up (also in terms of epicness). If it was just a general, but stronger Getsuga with less side effects I'd see your point. Look at Naruto and the Gai VS Kisame or the Rock Lee VS Gaara fights for example. They had to use their self-destructing techniques, because their enemies forced them to either because they were too strong or driven them into a corner. Ichigo may have suspected that Aizen would be almost impossible to defeat without multiperforating him, but he didn't even try to hit him with a normal Getsuga and sliced him only ONCE. He even got out easily of the circle prison thing of Hollow Mask Aizen. He risked everything without even thinking about weighing his options and put all his eggs in one basket WHILE he was dominating.
And this just made the episode that much less plausible and more importanly, epically unepic when it could have been the most epic fight of all in Bleach, which it clearly wasn't. IMO, it wasn't even final clash worthy.