Relevant in terms of the growth of the sport? It's Chuck Liddell. He was commercially more valuable and was the UFC's first real icon (Ken Shamrock kind of became one retroactively when he went to the WWE). Chuck (and Tito) were probably the first guys that people who didn't watch the MMA may have heard in passing or recognize.
Fedor was not the equivalent in Japan or even close to it. Sakuraba was the Chuck Liddell equivalent in Pride (probably greater). Fedor was not that famous in Russia either tbh, most Russians I talk to know Khabib, not Fedor.
No, the existence of Fedor doesn't mean that it got Khabib into MMA even if Khabib was a big fan of him. Dagestan would have gotten into MMA regardless for the same reason they are in many other combat sports.
Fedor is more like Kareem-Abdul Jabar. An all time great and GOAT candidate, but not really someone who was commercially a big deal.
Perhaps innovation could be a substitute for growing the sport commercially, but Fedor was not innovative enough I think. He wasn't the first well rounded fighter who fought at an elite level, though he's an early example of one(Frank Shamrock was probably the first guy I can think of). Certainly wasn't the first guy to obliterate people with GnP which is what stuck out about him early in his career.