Remember on day 2 a few players hit 15 and many more hit level 14, they did this a sample size maximum of 6,000 as no way to get more clicks on a single account. Not saying math is broken but they were on the extreme light side of the coin to your 2x effort without success.
Related we have a friend who used 17,000 venir and still not able to go from 12-18 when math says 2-3,000 should get you their. Ncsoft uses rng but I think there is more winners and losers than there should be and the system is slightly flawed. I saw an alt with 30 pieces craft x3 Elixers in one craft....and mains with 100 attempts only have 3 or 4.