"seemed unstoppable"
That's cute but delusional.
Tony barely made it through many of the fights even during his win streak, he was usually getting his ass kicked to barely survive and come back
Kevin Lee beat the absolute shit out of him but then gassed because of a nasty staph infection
Anthony Pettis beat the absolute shit of of him but broke his hand and couldn't continue
Donald Cerrone only lost because he stupidly blew his nose between rounds.
It was a miracle that Tony won either of those fights. He looked incredibly lucky, not unstoppable
And nobody with a shred of common sense thought he'd have a chance against Khabib. Khabib was always going to destroy him.