Heavyweight has definitely gone backwards, we've had maybe handful of guys with promising elite skillsets or specialists that have transitioned to MMA in the last 10 years such as Cain, Brock, Stipe, Blaydes, DC, Rosholt (bust), Konrad (retired early)....we don't see many high level grapplers / kickboxing crossovers transition like we use to. Pride / Mid Era UFC had Sergei, Werdum, Hunt, Cro Cop, Nog, Fedor, Coleman, Randleman, Barnett, Mir, Monson, Schilt. The talent in kickboxing has long peaked and wrestlers / grapplers don't seem to transition to MMA like they use to.
For the lighter divisions the sport has definitely evolved and I'd also say we are seeing more high level athletes that previously, we never saw guys with footwork or movement like Dillashaw, Cruz, Stephen Thompson, Holloway or FW Conor, everyone is definitely more well sound on the ground anytime strikers crossed over they were at best a developed white or low blue belt level. There was definitely some solid strikers like Yves, Pulver, BJ or Gomi but I don't think they had the same overall skillset as we see from the best strikers of today.