the single most influential person involved in the genre: John Carmack.

Why would an engine developer be responsible game design? Are you confusing the Johns and meant John Romero?

And what would the genre be called then? John-like?

boomers didn’t make the genre, boomers don’t deserve the credit.

Neither did Castlevania in Metroidvania. Metroid founded the genre a decade before Symphony of the Night game out, it’s just that it was called a side-scrolling action adventure. That’s a bit long, though, so a shorthand was needed.

Personally, I would not mind “Retro FPS” but it’s just a label and in the end doesn’t really matter much.