This isn't a real counterexample, but an interesting case is Bobby McFerrin, who wrote "Don't Worry, Be Happy". He avoided listening to singers for 1-2 years in order to develop his own voice/sound:

"First was the vision, then the technique of working it out. I wanted to find my own way of singing by knowing myself. I knew that if I started listening to other singers, it would take me years to develop. So I shut myself off from other singers for along time."

from page 25 of https://www.worldradiohistory.com/Archive-All-Music/R%26B-Re...

That makes sense to me. If I was about to write a doom metal record I'd probably avoid listening to doom metal for a while.

The difference here, as you point out, is that Bobby already had a lifetime of listening to music and appreciating other singers.

There are many game devs who don't play games. A lot of artists would rather be working on movies, and a lot of programmers who just love to program.

The best game devs all do though.

But are these game devs designing the gameplay loop? Or are they working on backend, like the engine?

I could imagine a (solo) game dev not self-describe as a gamer, but they must have some intuition about what makes (video/board) games fun and engaging.

I can't imagine you can obtain that without ever playing games yourself?