my thoughts were what if some heroes will be able to counter some other heroes
Very deep thoughts
The heroes have generally been enhanced a bit, and made more resistant in the Patch 4.1.
Gandalf, for example, regained part of his iconic strength and effect due to his role in the faction and Magic.
The heroes are also more resistant towards creatures and other heroes.
Keep in my mind, though, that, to counter effectively another hero, you should always use wisely the Hero Killers and their powers, which serve their role