I was thinking more of a calculated odds. So let's see if I can explain this clearly.
The subtype cost would be affected by the community's activity with them. With that said, an example would be like a week of Magic Doll rampage will cause the cost of that subtype: Magic Doll cards to increase this would make other subtype cost less so it encourages variety. Players will be able to purchase other subtypes and build files with those in theory this causes a cycle unless you know people are just hellbent on playing 1 subtype. It builds community or at least tries to build community participation since players will affect the card subtypes probabilities/cost.
So let's say you wanted to go Martial Artist, but your deck is rather incomplete. It would be useful for a player to try out that deck and see what they are missing because if it was popular you can check foltart for lots of example due to it's popularity. On the flip side if it isn't popular that week then it would be affordable and cheaper in the lotto so kinda win win.
Surely there is a way to do this since, there is an UD list which means in theory you can also see which cards are the most popular since you can see the least popular ones right? While I agree that different subtype have different pool size, I don't think it actually affects the ratio of rares within each subtype. (Okay maybe Adventurers subtype are the exceptions to this)