IMO Carrick is not playmaker and not since 2008-09 season where he used to go forward often.
Fletcher was never a DM. His best attribute was closing down opponents and he was all over the pitch (which people call here as Runner). Against Newcastle he played very disciplined role and if can do that regularly then we will have very good cover for Carrick or even better player.
Since 2008-09 season, Carrick plays deep, wins the ball and plays simple passes. That's one of the reason many (who didn't understand his role) bashed him saying he plays only simple passes. For whatever reasons Carrick has stopped playing expansive game, the discussion which we had in FMBase for years and everyone thought it was obvious change in role for him.