I figured out a decent strategy...
Vaegir Army is pretty much: Archers on hill tops and Infantry on slope. Rain until enemy is close, than charge.
I would usually put the cavalry on the left or right flank, and have them charge when the infantry charges, surrounding the enemy and feel like Alexander the Great (with his Phalanxes and Companion Cavalries).
The new strategy is to have the cavalry stand with infantry and Vaegir veterans, and have them charge together. As long as I don't charge too early, I get the same effect as the usual strategy. Vaegir veterans are assigned to infantry in this case.
It works pretty well in small scale battles. I have yet to test it on large scale battles (with couple ally and enemy armies).
Editing is great. But this play is on a Mac, and I can't find the file.
Also, I realized (on a different, end game play) that I kinda skip Vaegir Veterans with lvl 6+ training on 5 heroes. That's another way around it.