lvl 40 chest are full of uncommon and common items , it haves no sense , I invest from half an hour to an hour and a half per leg and all I get is trash items that are usually worst than the ones I...
It is a high score activity. Scores are based on whatever map has the highest multiplier, I think it changes every season? Check what map gives the most and do that, after doing a 30 wave impossible...
Unless there is a huge technical roadblock in adding more GM slots, there isn't a good reason designwise why there aren't extra GM slots, when about every game with a GM-like feature I've played...