Am a p2p player but still not have newest heroes. Why is this?
Right now the clever way to spend your money in the game is to purchase the Bazaar's packs. Those including new heroes.
Rolling heroes with gems is a matter of probability. Maybe you will get a new hero with a random 450 gems roll, or you will be rolling 50k gems and getting 2 Druids, 1 Siren and 6 Succubus.