No, they are mostly not inferior. Zotac has an excellent engineering team and they do cool things.
I personally recently switched to the EVGA for the GPUs as they have the best warranty terms and excellent support.
In fact, Zotac AMP! Extreme cards are awesome and can be compared to EVGA classified/FTW only.
Regarding the pricing - Asus is top tier vendor and the other two are "wanna be top tier", so they set the pricing accordingly.
I don't like the GB engineering and cooling solutions as they were very loud (no recent experience though).