Carmack is a genius no doubt. But genius is the result of intense focused practice above and beyond anyone else in a particular area. Trying to extend that to other domains has been the downfall of so many others like him.
Funnily enough Romero himself didn't ship much either. IMO it's one of the most iconic "duo breakups". The whole is greater than the sum of the parts.
Romero is credited on 27 games since he left id Software.
If you examine the list it includes games like "Gunman Taco Truck" by his 12yo sun, SIGIL I/II (Doom mods) and a remake of Dangerous Dave. Most of the money he made post-id came from Facebook farming games.
I'm not saying he's doing nothing. He's extremely talented and achieved more than most of us could ever dream of. I'm just pointing out that after he departed from id neither id nor him managed to replicate the earlier success. Who knows, maybe times had changed and it would be the same even if he stayed.
Duke Nukem was released in 1996, then Unreal was released in 1998 and that's when they lost their technical advantage. The market became saturated with FPS.
Romero and Tom Hall founded Ion Storm which produced one successful game - Deus Ex. He gave up on AAA and went back to creating small games.
Carmack's licensed code was the basis of many successful games beyond the 90s, including Half Life 1 and 2 and the latest Doom games. We wouldn't have Half Life without id Software. Maybe Valve Software wouldn't exist.
Graphics rendering and AI live on the same pyramid of technology. A pyramid with a lot of bricks with the initials "JC" carved into them, as it turns out.
Maybe someone better at aphorisms than me can say it better but I really don't see it. There are definitely mid-level low hanging fruits that would look like the kinds of things he did in graphics but the game just seems completely different.
He's also admitted he doesn't have much of math chops, which you need if you want to make a dent in AI. (Although the same could have been said of 3D graphics when he did Wolfenstein and Doom, so perhaps he'll surprise us)
I wish him well TBH
So, his initial tech was "Adaptive tile refresh" in Commander Keen, used to give it console style pixel-level scrolling. Turns out, they actually hampered themselves in Commander Keen 1 by not understanding the actual tech, and implemented "The Jolt", a feature that was not necessary. The actual hardware implemented scrolling the same way that consoles like the NES did, and did not need "the jolt", nor the limitations it imposed.
Then, Doom and Quake was mostly him writing really good optimizations of existing, known and documented algorithms and 3D techniques, usually by recognizing what assumptions they could make, what portions of the algorithm didn't need to be recalculated when, etc. Very talented at the time, but in the software development industry, making a good implementation of existing algorithms that utilize your specific requirements is called doing your job. This is still the height of his relative technical output IMO.
Fast Inverse Square Root was not invented by him, but was floating around in industry for a while. He still gets kudos for knowing about it and using it.
"Carmack's reverse" is a technique for doing stencil shadows that was a minor (but extremely clever) modification to the "standard" documented way of doing shadow buffers. There is evidence of the actual technique from a decade before Carmack put it in Doom 3 and it was outright patented by two different people the year before. There is no evidence that Carmack "stole" or anything this technique, it was independent discovery, but was clearly also just a topic in the industry at the time.
"Megatextures" from Rage didn't really go anywhere.
Did Carmack actually contribute anything to VR rendering while at Oculus?
People treat him like this programming god and I just don't understand. He was well read, had a good (maybe too good) work ethic, and was very talented at writing 386 era assembly code. These are all laudable, but doesn't in my mind imply that he's some sort of 10X programmer who could revolutionize random industries that he isn't familiar with. 3D graphics math isn't exactly difficult.
Also, I think most of the x86 magic was done by Abrash.
While this is certainly true, I'm not aware of any evidence that Carmack thinks this way about himself. I think he's been successful enough that's he's personally 'post-economic' and is choosing to spend his time working on unsolved hard problems he thinks are extremely interesting and potentially tractable. In fact, he's actively sought out domain experts to work with him and accelerate his learning.