The difference is that O'Malley has charisma and colorful hair.
I don't find O'Malley charismatic, at least, lately. I find DDP very charismatic but for some reasons, he is one of the most hated fighter by Dana White. Merab isn't charismatic but his fighting style is very entertaining for me, I love showboating. There are some other charismatic fighters but truth be said, there is no one like Conor McGregor and will probably never be.
Compared to the fighters I mentioned, O'Malley is the most charismatic. But compared to the others, he's equally a door. And I agree with you, Connor was something unique. Currently, I only think of Poatan with his "Chama," but it's far below what Connor did at his peak.