I think the ranking system is good. I like it.

But in order to encourage members to play, a reward is necessary.

Something like "the higher position", the player earn more coins or heal kits or money. You could classify in different levels, e.g. 1-100 will get 1000 coins, 100-1000 get 500 coins.... The periodicity could be every season.

Furthermore, the player must have a minimum of matches in the season, such as 10 matches, in order to earn the coins.