Meh. 1 damage for five?
This is a game where most creatures have less than five attack. And by most, I mean almost all of them. Will edit in percentage.
Making it cost another quanta wouldn't be too big of a nerf.
EDIT: Of the 81 creatures in game (counting nymphs but not flying weapons), 60 of them will get one shotted by a lightning bolt. (this doesn't factor in growth or stone from, and upgraded, the number is actually 57). This means that roughly 3/4ths of all creatures can be one-shotted by Thunder Bolt for the measly cost of one aether.
Just needs a minor nerf.