[fictionfan]

Yeah,
Astral can summon imaginary creatures or creatures from another world.
Water can have a ritual spell to empower a unit with huge Def that last forever.
Earth creates some improved better golem
Fire or blood could have a kamikaze unit that sacrifices it's self to to kill a SC (like a Tartanian).
Nature could have a more powerful maggots for stronger mages (I do not think this is the best idea, but I am just giving possibilities)
Air could have a powerful spell that will blow the enemy army away (retreat)size negating.

What I am saying is every kind of magic needs a killer spell and/or to make diversity. It can't just be death that makes a army of SC.

PS: although in fairness wish is also a awesome spell