Saying that being on stage is terrifying and that coming up with banter is very difficult is completely your opinion, though. Just because it's hard for you doesn't mean it's hard for him or anyone else!
From a very personal point of view, I can't even count the number of times I've been on stage just in, like, this past year. I've always been a performer. I'm a zillion theatre shows and I sing for a zillion choirs, I'm in an improv troupe and I'm a musician who's done small gigs before. Listen, I don't get stage fright. Ever. I don't think it's scary at all, I love it. I LOVE being the center of attention. And banter? It's not hard, ESPECIALLY if you're a born performer, and you love entertaining people. Mika could DEFINITELY do it.
Stand-up comedians do. But their talent and job is crafting the EXACT structure, sound, and diction to make their joke the funniest. So when you find the perfect sentence structure, you have to repeat it every time you do your routine. But other types of comedy aren't like that. For instance, I'm in an improv troupe, so every night for us is something completely new and made up in that second.