To offer a contrary viewpoint, I think the Hero class would be rather balanced, so long as they didn't also have ridiculous stat growth. Being able to counter your enemy only works if you're powerful enough to be effective with it. 

Like, for example, a mage blasting a warrior is fine. Mages do big magical damage and all. But a Hero with substandard magic stats trying to do the same will just be rushed down by that same warrior, who can tank that amount of damage and then ragdoll 'em.

Could reword the class as 'Journeyman' or something. They have the ability to learn all sorts of skills, as a sorta trial run to figuring out what they really want to focus on, but because they're trying out all these things, they won't be as good in the future when they do focus on one thing they like, compared to someone who always knew what they wanted to train.