Okay, then, here's a question:
Why aren't you using heroes?
BTW: I think you should, but not Warcraft 3 heroes, with levels and stuff. No items, no ultimate spells, nothing like that, but base them off another unit and give them a different name. It expands possibilities of stories and stuff. But of course, the only downside of this is that they cannot be used in non-campaign missions (are you even doing a campaign?).
Example - In Warcraft 2, there's a mission where you've got to rescue Cho'Gall and escort him. Cho'gall is based off of the Ogre Magi unit, has no extra spells or anything and perhaps has a bit more health and damage, I think, but nothing overpowering.