Title defense is not a strong criterion. Why? Fighters get title shots at different times. For example, BJ Penn got a title shot after 3 fights in the UFC. Frankie Edgar had a respectable run to the title, but he has too many losses in the UFC at 6. Benson Henderson got his title shot after 2 fights in the UFC, and again, too many losses in the UFC at 3.
If Khabib had received a title shot after 3 fights in the UFC, then he would have been at 7 title defenses already. In comparison, if Tony Ferguson was given a title shot after 3 fights in the UFC, then he would have failed to win the title against Michael Johnson.
Khabib has a strong case for best UFC LW ever, and even best MMA fighter ever. For the people who claim Fedor is the GOAT for being "10 years undefeated," Khabib has surpassed that, and he did it in the best organization in the most talent deep division.
Conclusion, title defenses are a useless criteria to judge UFC greatness, because fighters don't get to fight for the title after a standardized amount of fights. Consecutive wins is a better criterion.