@Gambrinus: That's a good suggestion. However, then there is no need for a medal system whatsoever, and then the leaderboards will be dissolved.
The medal system is, I suppose theoretically, meant to represent different levels of dedication and skill in the game- which gives those in the leaderboard their 'elite' status.
If you rise on the leaderboard, you commit significant time to attacking all manner of bases, being victorious enough against most of them to maintain an elite ranking.
On the other hand, if you do not have the time or skill to rise in the rankings, you remain low in the leagues.
Forcing a player that does not want to compete in rankings, just because you as an elite player have decided to put yourself into a very small pool of other players, isn't particularly fair either. Level hasn't got much to do with the type of dedication and skill needed to get onto the leaderboard.
So in this scenario, if its level based competition you want, then the leaderboard becomes defunct and there are no medal rewards. That may upset people that have an extreme desire to be ranked on a leaderboard.