Think of it this way: the card you pick doesn't matter regarding the animation or where they end up.
You do not have a 20% chance of pulling each card equally, or the rate of success would be much higher. Instead, say gold heros have something like a 1% chance of being selected. Even if you have 4 golds and 1 white in the same roll, you still have a 96% chance of pulling the white card rather than one of the golds. It only appears to be an equal chance because of the visual animations and would be less frustrating and just as random if you got heros in the same way you rolled runes. The frustration is a result of how we connect the 'pick-a-card' animation to our expectations. It seems to defy logic, until you take a step back and realize the cards are just a nifty UI perk. There could just as easily be a big red button that you pay creds to press and one random card pops up.
A purple would be higher chance than gold, but still less than blue or white. The overall animation of the card you want moving left and right is a tease. There's only 5 cards, they have to go somewhere other than where you pick, and the fact they seem to always be next to the card you pick tempts you to pay the 10 gems for another try, even though the odds are still really low of actually getting one. Basically, the odds of selection don't have anything to do with your crystal-ball rubbing skills regarding which card to pick. Just like runes or winning the lottery, statistically the odds of picking one increase with the amount of credits you spend. However, the only way to really get the hero you want is pass up on useless ones to save spirit points. Alot of people get so excited by actually rolling a hero that they will recruit no matter who it is. Rhize looks good, but is he worth 3 mil creds just to end up back in your hero inventory once you have Adam? If you think the answer is no, 3 mil creds can get you more spirit points if you make the hard decision to pass up on him.
Essentially, planning ahead and managing creds goes a long way towards reducing frustration.



