Well...it regressed somewhat because, if I am being honest, back before 2012 everyone was on steroids, which provided us with a hell of a lot "holy ****" moments, but on the flip side of the coin, back between say 2002-2008 or so, MMA was no where near as popular so most fighters didnt just do this for a living and train 24/7. They had other jobs and MMA was a side job.
Case in point: Penn was the exception. He came form a wealthy family, which allowed him the (back then) rare opportunity to train full time in a time when that was unheard of. That MUST have given him an edge over his opponents.
Nowadays you have these lab grown killers that live, breathe, and ***** this stuff, 24 hours a day, 7 days a week. Training camps are full time 3-4 months jobs preparing for just a specific, single opponent. They are completely different kinds of beasts.