They are not. In Associations only the stars of your players (and your rivals' players) are taken into account. Otherwise you could only play together and against other players with your same exact level.
Here is an example:
User A is Level 10, has all his players with 5 stars
User B is Level 20, has all his players with 5 stars
Of course the real quality of their players is very different, the players from the Level 20 user are much more powerful in absolute terms. BUT in Associations, players from user A and user B would have all 5 stars. That makes Associations the perfect place to team with other Managers who have many different levels, which is the point of this feature: Play with your friends no matter what level are they. In Associations you always see players with the stars his Manager sees them, even if he is 15 levels ahead or below you.