This is not necessarily true at all. It’s quite conceivable he could get KOed in MMA. Even by non-strikers. Smaller gloves and the threat of takedowns changes everything.
Boxers had a very mixed record in K-1. They got KOed sometimes. And that’s without the threat of takedowns.
With TDs, even if the guy doesn’t go for them, you have to have a different stance and hold your hands lower.
Holding hands lower hurts your defense a lot. And the wider stance means jabs are much less important, as your power hand is much closer and thus more useful in MMA.
Guys like Cro Cop, Pat Barry, Overeem have got knocked out plenty in MMA. Even by grapplers.
MMA is just more random than boxing.