No xD it changes usually, when new players join the team (slightly at least, for example, a top scorer, rarely will stop scoring if we buy new players)
But for example I had a experience time ago, buying 6-7 STs, noone worked, and I used the Reserve ST, of 5*, Yordanov, and after face many troll scores vs -30%s+ suddenly, the team started playing well, I had the match control, and troll matches stopped.
This means, that at some point, I had inside the team, "al the contributive roles covered" so, I couldn't buy a new player and see him performing as a key player, or even good, because, there wasn't space for more contributive players.
I tend to keep a full squad, with 10 reserves that are my old players who I want to retire in my club, and it causes these stuffs... so if I "already have" the good players inside the reserves, I would need, to sell some of them, to allow new players to become key players.