Firas doesn't fight himself these days. He used to compete a bit years ago but for the last fifteen years at least he has been a trainer and cornerman of martial artists. Other than damage from the gym I don't think he's been hit that much in the head.
The thing with training in competitive martial arts is that your false bravado gets mercilessly picked apart and crushed to dust. Rogan's podcast occasionally has segments mocking fake martial artists, rightly ridiculing their obvious lack of real knowledge, perspective, or experience. It's astounding that he can't see that when he rambles potheadedly about some subject he googles sometimes he becomes that guy demonstrating how to catch a punch out of midair or kick a knife out of someone's hand. To anyone who understands the subject better, which is a low, low bar, he looks ridiculous.
It's annoying because I feel I've learned a lot from Firas and here he is making an idiot out of himself in front of a massive audience. If I ever try to talk about some of the great things he teaches, people may well just think of the guy who Dunning Krugered the living shit out of primary school level science that one time on JRE.