You are wrong. I have seen videos of people getting Roshi at 210 scrolls.

I myself got him at 190! (And 10 pulls later got my 3rd jinchuuriki rare ninja as a side note). So drop rates are not fixed. Also OP, its very hard for someone to know exactly how many pulles they did in kage, rare ninjas don't drop exactly every 60 draws, so sometimes people are off by 100 pulls (both more and less).