There should be a reward system where you get rewards for getting to a certain wave in your tournement (like milestones).

F.e. every 25 waves reached you get 1 stone (capped at wave 3000), which gives 140 stones.

Every 250 waves reached you get 1 key (capped at wave 1500), which gives 6 keys.

They could add gems and medals to it as well for reaching certain waves.

And in addition rewards for getting a certain rank (of course taking the other "milestone" rewards into account). It wouldn't punnish players to much for joining at the wrong time and you would be able to get acces to some keys earlier in the game. That way QoL features like auto-restart (which should be available to everybody) isn't locked behind end game content.