Matic is a good player who compliments Herrera and Pogba well. He's been especially good since Ole arrived. But I don't think he's undroppable. He doesn't provide midfield control like Carrick did. So many times even since Ole, we've seen players just jog past him which leaves a lot of defensive pressure on Herrera.
Matic might be marginally better at passing and against the press. But overall, McTominay might give us some more balance. Either way, Matic isn't good enough to walk straight back into the team and that's my point.