Your first point is well taken. You don't disrupt what's working. Ole's at the wheel and the ship is heading in the right direction.
But the second point has issues. On what basis can anyone say "VDB's time will come"? Who does Donny knock out of the starting XI? Not Bruno and not Pogba and he's certainly not a destroyer, so not Matic. Even if Bruno goes out for a month with injury and Donny puts in god-like performances, there's no chance Ole is going to relegate Bruno, or Pogba, to being Donny's cover.
There's no road for Donny to become a regular starter for us unless we sell either Bruno or Pogba, which is always possible but not likely, given the financial situation other clubs of potential appeal of clubs like Real and Barcelona. Sure, perhaps the club bought Ole this year in the belief that Pogba will leave in the summer of 2021, and that may still happen, but there's no chance Donny will push either Bruno or Pogba aside especially if he only gets 2-3 minutes every second or third game, decisions which are solely made by the manager.