If you do that you'll face the same situation I had, when I kept old glories inside my team till they retire.
I bought 7 STs, and I couldnt get a single decent player, ans then I realized cause it was cause I had top performers (1*, 2* 3* inside my reserves) waiting to retire.
There is a limit of roles, that exist to create realism, and cause the engine needs to lcreate a realistic football simulation so, the team needs real football events, goals, assists, fouls, corners, ao a rank of better/worst contribution and aggressivity too.
There are mainly 2 powers that we have to consider, one, is the Contributive power. The 2nd is, the Dominance power.
A live match have 25 animations, the more domination a player have assigned, the more slots he'll take. The more contributive power = the more efficency.
You can perfectly feel the differance between a fluid match and a stuck one.
If you buy a player with a lot of dominance power but low contribution, then is when the game looks like stuck, because there is a player who occupy a lot of space for nothing. So, its so important, test players and, discard them if needed.
You can realize too, that usually there are 2 situations; or a key player, (1) resolves the 70% of your games, or, the power is spread between a couple of players and alternating.
These players, key ones are basically those earning Top Ratings, and top ratings are 9's and 10's -are the same-
Then once you know how to identify your players behavior based on internal settings, you can try a next step, which is follow the rating patters to anticipate the next performance of your players, and too, as I do, manipulate ratings intentionally, to force "a push" at certain games, cause even the Key players, only keep the 10's for a streak of 2-3 games, and then another players alternate them as decisive players in a match. You can see patterns like 6-8-6-8-6 so after the 6 you can expect a 8.
So if you force a rating downgrade by keeping players that got a rating drop as reserves + playing with those who should get a drop, in the upcoming match you can have a push.
Practice.