Read the John Romero stuff. Even Carmack explains in the Lex Friedman interview how badly Carmack treated him. Carmack also presents enough in that interview to expect this take us quite likely correct.

All from Carmacks own mouth.

This is... confusing.

Especially considering that there are two (unrelated) Carmacks: John and Adrian, both cofounders of id software. As for John Romero, he did a lot of "stuff".

How is it confusing? The way Carmack treated Romero is famous, and the recent Lex Fridman interview of Carmack even has it admitted by Carmack. Carmack, in the same interview, explains how he is an asshole to people that work(ed) with him at Meta.

Listen to the interview, and see if Carmack sounds like a reasonable boos, able to get the best from his staff, or sounds like someone that would cause serious friction. I'd pick the latter, from his own description of how he treats people.

He's a good programmer. He'd be absolutely terrible to work with or for.