How about randomly mixing the posse rewards
What if you randomly mixed the posse rewards cards and then kept them hidden until the posse collects them. Not all posses are created equal and most people play for card packs or leaderboard bragging rights. I don't think any posse would quit because they gained a legendary card at 300k but it would give the lesser posses a chance at a useful card to help make them stronger !!! Just a thought !!!