This is also anecdotal and maybe the by-product of the circle I am in, but I don't see McGregor as a bigger name-value than Cena. It's not even close in South Africa, tbf. My partner's never watched a wrestling match in her life and she knows who Cena is. Opposite, she knows Batista (due to Guardians of the Galaxy) but didn't know that he was a wrestler before I mentioned it.
Apart from actual UFC fans and the Floyd/McGregor bout, I don't see any conversations about Connor at all in public or on social media. Whereas even Randy Orton is recognizable here because of the "RKO OUTTA NOWHERE~!" meme - so much so that there are still night club events being named after it or referencing it - last night being one in my city (an event with the slogan "like an RKO outta nowhere, we're back!").
A gross simplification but I'd wage if their pictures were held up to the random public the reactions of those who do recognise both would be similar to "John Cena!" vs "that MMA guy".