I have personally spent well over 4000 gems and I have not received a single purple hero. It is at the point everyone I face has 2-4 purple Heros. It's bullshit that I have spent(at least 50 bucks worth of gems) and I can't get what I need to be able to be competitive in the game. If you can provide some insight that would be great, I have watched many of my friends purchase one 3 pack of Heros with gems and get 1 maybe 2 purple Heros. They haven't spent a dime on the game, seems extremely unfair.
If you have spent 50 dollars but only rolled 4000 gems, you are probably buying nothing but the 2 dollar gem pack. Wait for a 15-20% sale, and buy all in one shot. 50 dollars could have been 9000 gems, and I'm pretty sure you would have got something. Unless you did do this, then where did the other 5000 gems go?