"Position-less" basketball requires players with different attributes on the court. Is it the old system with a 1, 2, 3, 4, and 5 or 2 guards, 2 forwards, and a center? No.
I have heard the terms called playmakers, finishers and transporters on offense and defenders, helpers and protectors on defense. If a player is only one of the above, we're referring to a role player. Two or more attributes means they are a hybrid with the more roles you play, they more value you can add.
Specifically on defense, we need another protector (but with more versatility. This is generally a "big" in the old vernacular and likely a 4'ish player in the old world. Someone in the role of Patty or N'dea Jones with versatility is more beneficial than Kenyal Perry from a couple of years ago that was just going to be a protector..
Versatility adds value, but you still need the base roles and the versatility allows you to be more than a role player.