It works fine for me. I put it on my duelist who goes and clears the flanks of geists once enemies are engaged. My heavies with around 40-60 resolve and 2-handers deal with the mass of Wiedergangers while my archers take care of Necromancers and Fallen Heroes with greatswords/axes. 2 Sargeants with rally to counter geists. One is not enough as sometimes rally fails and they get fatigued so I use recover whenever possible.
Anyways. You probably need more greatswords to fight 20+ zombies with geists. I usually go for 2 sarge, 3 archers, 3 greatswords, 1 great hammer, 2 macer, 1 duelist against that kind of line-up. Macers are great if one of the greatsword Fallen Heroes gets too close.
TLDR: Turtle until zombies are dead and spam rally with 2-3 sargeants.