2000-2007
Golden age started with Pride's 2000 Grand Prix imo.
Gracie, Takada, Sakuraba, Mezger, Vovchanchyn, Otsuka, Goodridge, Coleman, Shoji, Braga, Kerr, Inoue, Fujita.
Takada vs. Gracie.
Vanderlei Silva won his alternate vs. Bob Schrijber, but never got past alternate status.
All these guys were about "prime", with some recently departing UFC gold.
This is where the second generation really started, and we saw a professional fighter MMA mentality sweep through into a sport mindset, which would become foundationary to today's model.
But it was still young enough where the brutality of NHB was still on display most notably in guys like Vanderlei, Coleman, Kerr & Vovchanchyn, thanks to Pride's glorious ruleset.
From here on through 2005 it only got better, with other organizations such as WEC, Elite XC, Strikeforce, Superbrawl, KOTC, UCC, rising.
Imo, this began declining with the fall of Pride and subsequent fall of other organizations, and the rise of the UFC as a Mcmonopoly over the sport.
Arguments can be made for exact times and instances moving dates slightly, but generally this is how I frame it.
Thanks for posting!