That's the thing, we have a lot of players who can play in different positions & that isn't restricted to a game by game basis, it can happen in the same game.
As for DeBruyne, he can run the show in the centre, or he can do a specific job out wide. He is the best crosser of a ball at the club, so there is no reason not to use him in that role if the manager fancies it. Or against Barca for instance, Pep may decide that playing all 3 of Gundogan, Fern & Silva, is more solid & then use KDB as one of the front 3, but also dropping back into midfield with Sterling or Sane doing the same, to make a 5. That would be a pretty dangerous counter attacking unit, which can also pass it & press as good as anyone imo.