He's not a defensive midfielder anyway
We haven't played with a defensive midfielder for years. And most teams with five midfielders don't either. The midfield all work to defend, be it zonally or not.
He's the pivot at the base of the trio, who lays the ball off and keeps the game moving. The role Denilson should have played, but was too lazy. You have to work fucking hard in that role, because you have to be available all of the time, and you also have to cover off gaps left by other midfielders (which is as defensive as it gets).
He's done superbly well at it.