The importance of each ability depends on your team's strategy and the player's position on the field. You can see each position's "profile" on the strategy page.
If a player does not have the right profile for his current position, certain of his abilities might be higher than the required values. In this case, the exceeding part is grayed to show that it does not improve his performance in the current position.
If a player does not have the right profile for his current position, certain of his abilities might be higher than the required values. In this case, the exceeding part is grayed to show that it does not improve his performance in the current position.