Yeah, play a bit more.
Most of the things that scale with shards are obviously underpowered in the beginning, but vastly improve with a few.
I've been playing death a lot recently:
Wither - basic spell, -2 attack is moderately useful in the beginning. -10 atk starts to get you somewhere.
Curse - basic spell - when it hits (might have to shadowbolt a few times) that wildlands critter is a few hits from death.
Can't remember name - all hits = critical hits. Don't even need curse at that point, demolishes pretty much anything. Moderately high mana cost.
Infection plus any of the above = infect the entire enemy army. Fantastic for large fights. Mana cheap too.
Dirge/Contagion/Wail - with enough shards/levels they are very powerful. Problem is that usually by round 2 (or 3, sheesh) they're not mana efficient since half the mobs are dead.
Blindness - basic spell - With some dodge, this is almost as good as crowd control.
There are quite a few spells I never use - i.e. kill. Who has 200 mana for a single target with only a % chance? Now, if it only took 10% of mana for a failed attempt...
All the unit buffs, and city buffs - most are no brainers with some being more preferential than others.
Gilden just chased me with a 600 hp army, I got away by freezing the army. Getting re-inforcements in those 3 turns - rushing upgrades to the outpost and slapping him back to the stone age. Then proceeded to decimate his empire while he recovered. He tried to retake a city - freeze, rinse, repeat.
Even with the tip of the iceberg above, its definitely useful. I've been playing a melee/defender SOV with a bit of death magic and its been great.