I've noticed that a lot of the end game spells have this problem.
For example with the Torch Bearer's final level fireball spell (does 1,000 or so dmg on a 3 second cast time).
The problem with this is that by that point in the game, my regular attacks do 500 damage per hit and fire 1.5 times per second. Meaning that I do LESS damage with my final spell that I dumped fiveish points into than with my default attack.
Obviously, this is messed up.