I don't think Sesko would struggle for minutes, with the number of outgoing transfers Man United are forcing out and I believe he'll be able
to match just exactly how good Man United are as a team, he's not going to be their best talisman, but he's not going to be their weakest link either, in my opinion, if not for Amorim trying not to force him to start a game as demanding as against Arsenal for his debut, I think the formation is probably just as glaring for us now what expect the frontline to, and that's Cunha - Sesko - Mbeumo, there is no way Mount is getting as many minutes as does today without United going forward once Sesko is eased into the lineup, and Diallo also playing ahead of Dalot is another change I'm expecting going forward.
The minutes isn't going to be bad as you imagined it to be, just as I wrote on the EPL thread; the 3-4-3 formation is not going to accommodate all the players at the same time.
The 3-4-3 needs someone with offensive and defensive work rate to help the 3 men at the back - Amad can't do defensive work.