While not all the skills don't seem all that impressive, they still have their benefits without a doubt. But i think the real powers lie in artifacts. As for troops not being useful, far from it. Sure spells are nice, but they are limited in many ways and so are spirits, i prefer a combination of all to be honest, though i don't mind lobbing the occasional fireball into the fray
But i am curious as to how many upgradable items there are and what bonuses they might offer.
And while spirits are nice, they quickly tend to end up being only as useful as troops or even less so since you only have one per round.