Ill say it every time - he isnt a DM. If you stick Pogba or Bruno in that role and expect them to do a job, you will have mostly similar results. McTominay's biggest weaknesses are his defensive positioning and reading of the game, which are two of the most important attributes for a good DM. Its for this same reason that I dont think he can ever be a good DM - its not just little bits of his game that would need to be worked on, it is that the position requires pretty much the opposite of his skillset.
Fred has looked good when allowed more freedom and to get further forward. McTominay has also looked good when given that same freedom in previous games.
Bring in a player in the mould of a Carrick, Jorginho or Fabinho, and stick one (or both) of Fred/McTominay in front of them, and we will instantly have a far more cohesive and balanced midfield.