I have to assume this is not how it works, or it wouldn’t be so easy to find 10-12 players quickly (usually) to play ranked free-for-all.
It almost certainly looks further afield than just the players you happen to have in the same session. Most of whom statistically are probably not interested in the ranked mode (only a few thousand globally were ranked, last time I checked, and the chance of finding 10-12 from those, regularly, in your session of <70, would be almost nil.
To the OP, I also play on PC (only) and haven’t had the problems you’re having. So I’d check your settings as advised above. But at least you know now it’s not a problem with the PC version per se. It works just as well as the Xbox version.