This new leaderboard is ok I guess, cause it shows you are trying, but maybe it needs to be reimagined?
First, you could restructure it into a tiered system, maybe keeping the arenas themed levels. Perhaps you need to reevaluate and alter the milestone values of each tier if some players are scoring so much higher than the current levels. If you intend to reset everyone monthly to the same level you will discourage newer players from playing as they may be facing the top players for the first few days of every month. It would be better to reset people to the lowest value of their current milestone and have increased prizes for each milestone level.
Second, a prize system is absolutely necessary. I would suggest Introducing convenience type prizes instead of gear to start with, maybe a bit of coins or gems also. These can be anything from lock picks to speed up chest timers to some type of scroll of true seeing to increase the odds of finding secret doors in challenge modes for a limited time.
If you go with true seeing you could even introduce a second level of secret doors. You could keep the ones you have now and also add a second color of secret door containing a chest of slightly better odds. These type of secret doors should only be found while true seeing is active.