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.
I know that people find him charismatic but I personally don't find him charismatic. I mean, he tries to be but it's so fake for me, he is not the type of the guy he tries to show us. As I understand, people mostly love him for smoking weed, for his pink colored hair and tattoos.
I forgot to mention Pereira. He is a unique fighter. He doesn't speak much and doesn't speak English too but he manages to sell fights well. The way he looks already sells the fight, that stoic face is enough. I like Pereira, he is an amazing fighter and human being.
Guys, there are rumors that the next Lightweight title fight will be Topuria VS Gaethje. I think that this fight makes sense. Ilia will either fight Holloway or Gaethje. The next might be Arman and Paddy.