I don't know if they have fixed this since the last time I have seen it happen BUT you do not have to deal damage during the banish to win the 10mil. If you come in during final fight- 0% damage dealt- you can "win" the ten mil. Most major issue with that is that if you have dealt no damage and win- you don't actually get the 10mil which means NO ONE gets the coins for final blow. (Of course, if they have fixed this then nevermind.)

I'm on page with Revan; it seems like it waits for a certain amount of hits to be done and damage dealt doesn't have anything to do with it.

Also, I do not think that lower players who just happen to stroll in have a higher chance of winning. Yes, it happens but haven't seen anything to make me think the system is biased towards them.