Barbarian magic suppression skills...

A strong creature?! Maybe, but not against Orcs! They will happily devour it with any stack. The same applies to all other summoned creatures, except perhaps for the Avatar of Death, and even then, only if the hero is level 25 or higher. The only thing that Summoning can help with against Orcs is duplicates! And Anti-Summoning doesn't really help against them.

Then imagine a large stack (or even a very large one due to Necromancy and the Converter) of Lords under a Shield with 2000 HP, which absorbs half the damage. And the Lords not only deal damage but also, for each Drain, subtract 90 additional points of Rage. Or a mage can cast simple mines under a Sign, and 16 of them will appear on the field at once. A constantly moving Orc will take a beating, and that's about 250 damage from each mine. A total of 4000 potential damage per cast.
Moreover, magical races get 2 spells, while an Orc won't get 2 filler spells. But the problems with Suppression don't end there, because, by maxing out Darkness and Summoning, the Necromancer and Warlock easily acquire perks like Haste and Stone Skin. Mass Haste (1.3x) and Slow (0.7x at maximum Suppression) mean the Orc moves 2 times less often. And Confusion remains a fairly effective spell.