Fair point, but I don't know if this is as much of a change as you're saying because all three (Grealish, McTominay and Bruno) are fairly hardworking midfielders and can cover a lot of ground. We're not carrying a proper #10 here and the only real question mark as you say is if McTominay will be able to function as a pure DM. I personally think these players are flexible enough tactically to implement a system like this.
What do you think the system will be if we do sign Graelish (and Pogba leaves)? If we use our current system, it'll have to be:
---------------- Bruno ------------------
--- McTominay --- Grealish ----
in which case I don't think Grealish will be the right player at all.
Personally, I'm all for the signing of Grealish if the price is right. 40-50m is a fair amount for him. If its 70-80m we need to look elsewhere.
If we do sign him, we have to either play him on the left side of midfield 3 or in the AM position. He can be a backup for Rashford in the LW postion too.
IMO
--------- Bruno ------------------
--- Fred ------McTominay ----
looks better and more balanced than:
---------------- Bruno ------------------
--- Grealish --- McTominay ----
McT has good working relationship with Fred on the pitch. Dismantling them to fit Grealish would be daft if you ask me.
It also looks better than:
----- Grealish ------ Bruno --------------
---------- McTominay/Fred -‐---------
So the question is are we really going to buy him for 70-80m and have him sit on the bench? On top of that we need to re-mould McT into an anchorman and drop Fred?