John Deacon (Queen), Roger Waters (Pink Floyd), Cliff Williams (AC/DC), John Paul Jones (Led Zeppelin) all flatwound users.
Rotosound flatwounds seem to predominate.
Here’s the thing. You can find any genre, and I can find a bass icon who uses flats or rounds.
They say you need flats for jazz and/or fretless. What did Jaco use? Rounds.