You're telling Pogba to drop into a midfield two along side McTominay and be a competent, reliable player defending the middle of the park? That's not going to happen and is a reason why the side is unbalanced in the middle no matter who plays there. McFred have been the most functional duo, even if they are the least talent. This year, they haven't hit any form individually or collectively. It's still a work in progress.
United are usually outnumbered in central midfield because there's only two of them in there, when most teams will have 3 central midfielders..or in Chelsea's case, they have 3 CBs and can play 2 CMs. Teams let United's CBs have the ball, as the CF or other forward players are marking out the 2 CMs and funnel the play to wide areas. Pogba drops deep to collect, same with Matic.
United are one player light in central midfield as they really need to consider going with 3 CMs who play closer together on and off the ball. And their spacing on the ball and off the ball, which develops their shape, has been too soft for the most part this season. At times, they are compact and are better, but not enough.