He's really far right, a Jim Jordan acolyte. The MAGA wing is extremely happy with him. This is just some guy being extra racist, doesn't make Johnson a moderate or anything.
The modern GOP has such intense, strict purity tests that no one can satisfy them anymore. Pointing out an uncontroversial fact about the real world -- for example, that his black son is going to face more challenges than his white son because of unfairness built into society -- is enough to potentially crucify him even when he's otherwise a extremist.
Just another clear indication of the fascism that is cornerstone to their movement.
It's not just one critic though, it's several of the more prominent right-wing media personalities. I doubt it has legs, but it's scary to see how much vitriol they have against this guy who ticks 99% of their boxes.