Shouldn't progressive bands be, by definition, challenging institutions and forging new territory. The fact that "prog" bands all sound alike is almost ironic.
You are correct and should probably check out a book by (one of my closest friends) Jeff Wagner on progressive metal where he points out how much more truly progressive Enslaved and Voivod are when compared to the 1000 bands that try to sound like Fate Warning---
[ame]http://www.amazon.com/Mean-Deviation-Decades-Progressive-Heavy/dp/0979616336/ref=sr_1_1?ie=UTF8&qid=1357805878&sr=8-1&keywords=mean+deviation[/ame]
Personally, I like my prog and metal separate, but I agree with this point about the nature of progressive music and the irony of it becoming a genre.