As time goes by the book is growing on me. One turning point was realizing that not only could Demigryphs kill Mournfang and enemy armored elites in a cost effective way, but they could even grind down things like stormvermin hordes and actually come out on top, point for point. So I'd say Demigryphs are very compelling. They're also one of the few units we have that can execute its mission without magic support.
And given how dependent everything else is on magic, the Hurricanum is also very compelling. An extra power dice to fuel prayers and magic buffs, along with its innate buffs, could go a long way.
It seems to me that Empire is strongest as a magic-dependent close combat army. Shooting might still be effective but you'd have to engineer your magic around it, going with the lore of shadow to make those strength 2 mortars actually do some damage.