Heroes don't always gain skill points from leveling up. As heroes can level up to level 10,000 at the moment, it would cause heroes to have crazy skill point numbers that out match any troops. Instead as they start reaching level 50 we reduce the amount of skill points earned from leveling. The number of levels between skill points increases after level 50. Instead we give Gem Masteries at every level (up to level 1000).
However other than leveling up, heroes are able to get more skill points from unlocking and leveling Hero Classes. Hero Classes give skill points based on the class so a Knight will give a lot of Armor but a Warlord might get less. We use Classes as a another means to customize your hero.