Some interesting comments from Whitaker
Rob is by far my favourite fighter. Such a normal respectful guy that is an animal in the cage that always has great, exciting fights. Just a pity that his injuries stopped him from defending his belt much and then Izzy came along who is just a better stand up fighter. Still Rob has gone through Till, Jared and about to fight Costa (I think he'll win) to get a rematch, so regardless of his first showing it'll be more than deserved. I don't think he'll win but I think he can win, if that makes sense?
If he beats Costa then he'll have beaten:
Romero x2
Jacare
Hall
Tavares
Brunson
Till
Jared
Costa
For me that puts him in hall of fame reach regardless of if he can beat Izzy. One of the best Middleweights ever.
Anyway in terms of your post Khabib might not be the GOAT but for me he is the most unbeatable fighter ever. It doesn't matter what your skills are because he just negates them. Basically if you could imagine a Khabib at any weight class in the UFC then nobody beats. As in a Khabib the same size as Usman beats Usman an a Khabib the same size as Jones beats Jones. Funnily enough the only slight doubt I'd have would be a Khabib the same size as Mighty Mouse.