It would just negate a reputation that he has worked his ass off his entire life to build if he hasn't done valuable targeted work on the visuals of the device.
All I'm saying is that there is a path through which everything Carmack said could be true, and also the latest hardware doesn't really use what he built.
But I have a return volley for you...who on the Facebook/Oculas graphics programming team, knowing that jcarmack was your boss, wouldn't go full nuts on trying to create some slick tech to impress him with? I'm sure FB has the pick of the crop when it comes to hiring talent, and at least of few of those guys would have to be his fanboys and come up with very useful optimizations and enhancements to add to the Quest graphical stack, right?
The competency of FANG engineers in general is highly overrated. They are humans. They don't have access to some kind of forbidden knowledge. The idea that these companies are uniquely competent such that competitors don't even have a chance is largely a marketing story.