Ok, I found out what helps against >400 Devils supported by ArchDevils, Heliophagous and friends:
Fighting in Cold3, casting Army of Gold, Fog Warriors, Wrathful Skies, Murdering Winter, Warriors of Niefelheim, Storm Warriors, Doom and Weapons of Sharpness a couple of times, as well as bringing along 2 squads of mechanical men and two iron dragons, 3 raw tartarians, 1 healthy and proper equipped tartarian and 2 proper equipped AirQueens and cool WraithLord...
But one thing still puzzles me: Why didnt my army rout as they've done before? In previous battles, the AirQueens did almost nothing, for after their 5 turns of buffing & casting, my whole army routed before they waded into meele. This time every side fought to the very end. Why? Did it matter that I had a single berserked unit in my ranks? Again, scores of blizzard warriors (caelian archers) routed and left the high seraph communion (via crystal slave matrices 8 slaves, 3 serpah crystal masters in Earth, Air & Water, 2 relief druids) without any protection...the devils got dangerously close!), but this time, the whole army remained. In those previous battle non-routing mindless like Siege Golems were present, but no berserked units...
Seems like having a single berseker is vital if this is true. Or am I just obersving some odd chances?