Y eah, there was a season wehre I bought like 5-6 Strikers, and I realized that all of them couldn't be key players or even decisive ones because all the power was set on my reserves, that were old key players... so I had to sell them. Then the engine have free internal contributive roles to assign again, and these roles are limites to create realistic teams... that's why you cant buy 11 players that scored 40 goales with the previous team and expect the same...
Technically a player that comes from another club isnt the same because the contributive power he have is assigned once he join your squad, so... that's it.