User blog comment:IamJakuhoRaikoben/Chapter 431 & 432: My sword is... & Brair in Love, Review./@comment-5894890-20150429033859/@comment-25324252-20150429034954

Here's the difference, Aizen is awesome No but seriously. Aizen was built up as stronger than anyone else. He was supposed to be that unbelievably powerful up until his transformations, thats when he got bad. But as just a Shinigami, he stated he had reached the limits of a shinigami. Ichigo needed to be more than a Shinigami to beat him, which is why he needed to be a Visored. What should have happened was Ichigo mastering his hollow powers and defeating him that way but Kubo messed up.

On the other hand, you have Erza, who won a fight where she had no ability to see, hear, smell, feel or anything. She had no way to know if she swung her sword or if she even stood up. Aizen had explanations for how he could do everything, Erza has no explanation other than "She's Erza". Natsu is one shotting people who are supposed to be such a threat that the council had to step in. These are people who should not be one shot but they are.