In the battlefield,the value of King's Alric army is set like this: Berserks are the best for assult(and it's like the modern special seals.That's why they always go in the hardest misions.Remember the Watcher,Last battle,Ibis Crown,e.t.c)
Warriors are good for defense but they doing also well in attack mode,they are vital army unit,but they can't compete with the Berserks.
Heron guard now,are more specialized more training and much more experience units than Warriors.So they can confront better than Warrior the units of the dark.
It's right to be the royal guard and so the elite army under King Alric leadership,because Berserks aren't the tactical infantry.
They may have the hardest training(just remember,the pre-game picks on MYTH2,the Deceiver which the weather was really bad and they still wore almost nothing or the intro on MYTH TFL.It's shows their amazing abilities.But they are few and have no such a good matters.Usually they don't obey to the tactical orders and take the risk!!!
So the can't fit in this position.
I think that everything is set in the best way.
As for the past-please correct me if I'm wrong-I suppose that the army was set with Heron and Warriors for the humans,so Heron guards was the royal/imperial guard and the Berserks didn't make their appearence as long the tactical army(Warriors) could set all the problems.
P.S:something extra/else,can anyone tell me if the Summoner could arise exept Myrks and Myrks Giants? And if that was yes why he didn't used them against the army who went to destroy him?
Thanks for listening me.