The discussion is why can some players who are a 10 or an inside forward able to play as 8’s (Bernardo Sliva, Havertz, McAllister, De Bruyne, Foden, Bellingham) examples off the top of my head (I know McAllister is playing 6 atm) and others can’t? How much of it is tactically or position inflexibility or the manager not setting up the team properly.
And yes I am wandering my Mount or Bruno can’t play as double 8’s like the rest mentioned can.
Then it’s the second part of my comment: Mount and Bruno doesn’t contribute enough defensively to work well as 2 8s, it leaves Casemiro, who is only getting older, and challenges pretty rash, very exposed.
It only gets worse when you consider that Rashford doesn’t contribute much defensively and Anthony, despite tracking back, is as useful as a training cone. Compare that to Martinelli who is pretty effective of a presser and Saka, who has played LB and generally very solid defensively for a winger. Utd’s personnel does not allow for 2 very attacking minded CMs who don’t do too well defensively.