Though your info is correct (people overestimate their ability), your conclusion is invalid and a missunderstanding of the data.
Just because people overestimate their ability does NOT mean imbalances do not exist and hence that nerfs/buffs are not required. It simply means that *some* of the complaints can be ignored.
The *fact* is that (due to the fact that classes are not all identical), imbalances DO (and in fact must) exist.
Your conclusion is just as wrong as the people who are incorrectly claiming that they are amazing and hence class X needs a nerf.