Level of competition (at the time), number of title defenses, avenged both losses, titles in 2 weight classes, professionalism in and out of the octagon, embodies the martial arts spirit, retired on top, superb overall skill level in every aspect of MMA (striking and grappling), the list goes on..
Khabib hasn’t fought at the highest level possible imo, he is HUGE for his weight class, have missed weight before, never went up a weight class, has very few title defenses, not a complete martial artist (poor kicking skills, pretty much same playbook every fight, forces opponent to the cage, take down and GNP, rinse and repeat, he’s not even in my top 3 tbh.
Fedor and Silva are in the same boat, retired wayyyy too late, both aren’t as complete martial artists as GSP (Fedor lacks kicks, Silva lacks the wrestling), too many losses overall to be GOATed.
DJ matches up with GSP in almost every category , skill, record, has beaten everyone he’s faced, carries himself well outside the octagon. The only thing lacking is the level of competition he’s faced and also have not gone up a weight class.
Jon Jones is the only fighter that is close and may surpass GSP, if he wins it all at HW IMO there is not doubt he is the GOAT. Highest level of competition faced, overall skill level in all aspects of MMA is superb, perfect record, the only knock on him are his antics in his personal life, other than that Jones is without a doubt the GOAT behind GSP, if he wins title at HW, he is unarguably the GOAT.
There’s no debate, GSP is the GOAT FOR NOW.