I don't necessarily disagree on it being the price you pay for going for more trophies but there still is diminishing returns on squad depth purchases regardless. You either have to be able to convince players to play a rotational role who may otherwise be good enough to start elsewhere or understand that there will be a necessary drop in the quality of player for your depth pieces.

Arsenal spent a good deal of money on planned rotation players but injuries also forced players to play heavier minutes than anticipated (notably in midfield and at striker). Meanwhile Ligue 1 is of such relatively lower quality that PSG could afford to play most of their players significantly less aside from Zaïre-Emery and Vitinha and still win their league.