Healthy competition is fine, maybe having 1 on the bench who wants to play every week, and 1 who's not expecting it but is busting a gut trying to get into the team.
But if you have 2 on the bench then even shared evenly they're all missing 40% of games, and we aren't going to be able to bring on 2 attacking subs every game either.
Raheem has talked about being unhappy at his play time last season, and he played 47 games! He was unhappy because he only started 24 league games.
So imagine how he's gonna feel if he plays less than that 2 years later? Sané would be the same, and Jesus - Aguero even worse because he's Sergio bloody Aguero, and Sanchez if he comes would be the worst of the lot.
I don't have any idea what Mbappé would be like after moving for £80m+.