Yes and no, in my opinion.
Many times the difference between an average player and a "GOOD" player is confidence.
I've seen the difference in a player that is the best on a bad team...then goes to an above average team where he is ONE of the top players...and the difference is amazing.
Confidence his team can make a play, confidence that if he has a bad day at the plate, they are still going to hit the ball..that does wonders for many players.
On the other hand...
I have seen better than average players get on a GOOD team and they seem to get intimidated. They'd rather fly under the radar than go all out.
I think it depends alot on the player.