What I was thinking (just for example): Every bot has a certain amount of points attached to it based on how hard it is. The more points a level has total, the higher its tier.
(Still just for example):
< or = 500 points - Bronze Tier
501-1000 points - Silver Tier
1001-1500 points - Gold Tier
1501-2000 points - Diamond Tier
2001-2500 points - Titanium Tier
> 2500 points - Just... Don't Tier
Again just an idea, but thought I would share! :D