Barbarian magic suppression skills...

Regarding other factions... I don't use any filler units. I prefer to take Barbarian Luck and find artifacts (which isn't that difficult).
I calculate my skills in such a way that there's no room for filler units.

You're wrong! They'll overwhelm you with massed Darkness units:( And if your opponent is a Knight and pumps up Light? How will magic resistance help you? Believe me, I've checked it many times – a Knight with Light simply "tears apart" an Orc.