I'd argue that a lot of his success was directly related to not knowing anything about SQL/RDBMS because they were not required by his specialty.

Instead of spending time learning SQL, which he'd never use while creating a game, he only learned and practiced the skills he used for games. It's incidental that a lot of those skills are fairly universal and low-level, which gives us the false impression that Carmack is a generalist.

Why not? He doesn't need to use it for his work, why would he spend time learning it vs learning something relevant for his field? Oh, I know, to pass a GYMAAAE interview, but that is a pretty bad reason.

There's a universe of programmers that don't work in the LAMP stack (including me) because it doesn't suit what they are trying to accomplish.