Not sure you understand how modern football works...Grealish, and I would be okay with Rashford losing his starting berth. The front 5 would necessarily rotate where they play.
Pogba will be gone soon, I don't see us giving him a new contract, this is Matic's last hurrah (hopefully). I'm anti-Fred, so he should not be included in future plans, in my opinion.
No idea if Diallo is going to be an answer to anything, but if so, then Martial and Rashford will compete for one spot. We took a punt on Pellistri and because he was loaned out straight away, we should probably view him like any other youth prospect (i.e., don't get your hopes up).
Bruno chases the ball anyway, so McTominay would be more of a defensive midfielder, Grealish would operate on the right or drift inside, interchanging with Rashford. I'm going to leave the CBs and keeper as is.
From front to back:
-----------------Martial---------------Cavani----------------
Rashford-------------------Bruno---------------Grealish
----------------------------McTominay-----------------------
Shaw-------Maguire-------------Lindelof-----------AWB
------------------------------DeGea----------------------------
with Diallo:
-----------------Rashford-------------Cavani----------------
Grealish------------------Bruno----------------Diallo
----------------------------McTominay-----------------------
Shaw-------Maguire-------------Lindelof-----------AWB
------------------------------DeGea----------------------------
Those teams are outrageously unbalanced and would be torn to shreds by any half-decent pressing team.
I get people being desperate to get Grealish. Really I do; anyone can see how good he is. But that doesn't change the fact that we have no obvious position for him. Look how much trouble Griezmann caused Barcelona's system when they bought him without any idea of how to play him, and his two best positions (CF and RW) taken up by their two best players.
We're trying to have a team that can win the league next season. We should be looking for the final pieces of the puzzle, not signing a player that will force us to change our system. We have an obvious hole at RW (Greenwood is a forward, not a winger), and an obvious lack of quality at CB. Those are our two biggest priorities. Fix those, and our side is perfectly balanced and I believe is genuinely good enough to win the league. Grealish is a dangerous distraction who a feel will unbalance the team and cause more problems than he will solve.