Not enough hit points. But the Sorcerers are good. :)
And I'm curious, how is the comparison being made? Personal preferences and feelings?
In Heroes of Might and Magic IV, almost 50% depends on the hero!
I once leveled up a hero on a standard map so much that he could win a battle against 100 monsters of the highest level (except for black dragons) all by himself (without an army).
But, if we exclude the hero, then the Haven troops are still a bit weak, IMHO. :)