If HE really are C or D tier, could we add +1 MA to Martial Prowess and MMastery and see how it goes? or is that too drastic?
It would be a lot easier than editing individual units. Maybe I am just being lazy.
Also, what about magic damage on Silverins. They could have the same concept as silver bullets but instead they have silver spear heads. This could be useful in a number of match ups, and you don't need spears against dwarves. Could be lore appropriate if the agents of Yvress had magic piercing tips to combat demons, and would give them more of a unique niche to perform in.