I have no idea how you guys are pulling but i thought this was already common knowledge. the size of pull has an influence on the rarities you get. if you do single pulls/small size pulls the chances to get something rare drops.
I have used 200gran pulls (20 cards) and got a 3* tripler every time(100%). I made no good experience with lower pulls (10, 5)(0%).
I could accumulate 4 x 3* tripller Card this way.
My imput gran is a bit hard to calculate as I have recycled some Cards i will for sure not be able to use for the next 2 -3 years but i can say as Long I spend the gran at once I get 1 tripler for every 200 gran. On lower pull size i only make losses.