Auto-translated
I was just thinking. We could diversify the heroes: like in Heroes 3, divide all heroes into two classes – more magical heroes and warrior heroes. And, say, prohibit warrior heroes from learning level 4 and 5 magic spells. And prohibit them from learning certain magical skills. Because now, you take a hero whose attack and defense are mainly boosted, teach him magic, increase his magic power with artifacts, and there's almost no difference. Instead, give magic heroes the ability to cast spells more often without spending skill slots, and make the magic more powerful. Otherwise, it's not worth playing as a magic hero in Heroes 5, because his attacking skills are weak, and magic doesn't really help much.
Also, we could develop the idea of the three groves from WoG, with commanders. Create three types of commanders – archer, warrior, and mage – and give each their own skills and artifacts, like in the game Eador. Those who have played it will understand.