: Shouldn't the Heron Guard do better against the
: Myrkridia? They are the finest soldiers in the world
: of Myth.
Another part of the difference is that the 'krids aren't soldiers. They're not even human. They kill out of pure (evil, admittedly) animal instinct. The Heron Gaurd very well may be the best warriors in the world, but that doesn't mean that if you drop them in shark infested waters, they'll emerge victorious. The 'krids are simply too fast, too vicious, and too gaddam impossible to kill for any lone (normal/non-legendary) human to beat. They're demonic killing machines.
Another part of the reason is the demon part of them. They're "nightmares made flesh," literally a kind of living demon. A normal human probably can't beat a demon, y'know?