One of the best things about Koeman, rewatching some highlights is that, unlike EV, the defenders don't pass when they have space they can gain by advancing on the ball. That's why you see them often in the opponent's half, on build-up acting basically like central midfielders. De Jong, in many ways, playing central libero in the backline, is in many purposes on build-up a faster Busquets. Busquets doesn't drop anymore between the central defenders, because a large part of this role has been taken over expertly by De Jong, with the benefit that he is already facing the game and is much faster than Busi. So the move is reversed. Instead of having a DM dropping all the time to pick up balls, now you have a defender playing deeper theoretically, but breaching in midfield anytime there's a gap. And he does this very frequently to the point that you can't even consider him a central defender.
Under EV there was a tremendous amount of unprovoked passing from central defenders (usually to lateral fullbacks, almost each game Alba and Roberto both registered the most touches out of anyone on the field), which played a part in the boring football we played usually under him. Resulting in a very long team from defender to striker and in few options on the ball, because central midfielders rarely joined the offense.