I disagree with sweatyboatman on this.
Heroes are A focus, not THE focus of the game. One should be just as competent in warfare if he/she chooses not to opt for a nuking super hero, however this simply isn't the case in this game.
Currently, a master fire mage will wipe out any army of whatever strength in both Strategic and Tactical level. (Pillar or Fireball)
In my opinion, the Strongest Hero should only be 2X stronger than the strongest unit(i.e. being able to barely kill 2 really really well upgraded troops at the same time).
However, this will without a doubt tick off many players.
Heres my proposed solution that I think is a good compromise.
Have the ability to assign Body Guards to your Hero. Your hero can only kill one soldier at a time, however, your bodyguards, can also kill too.
I.e.
If your hero deals 50 damage, while your body guards deal 10 damage, and you have 2 of them (forming a group of 3) attacks another with 10X3 health.
Your hero unit wouldn't be lamely only killing one of them at a time, and would instead killing all 3.
But heres how it differs from the original. Since your hero unit is now a UNIT of 3, the body guards that make up the extra health, can die. And when they do, so does your hero units ability to rampage.
Spells should be reworked in general, to prevent complete utter destruction of entire armies on the first turn.
But thats a different subject all together.