The spells do different amounts of damage, and the enemies have different amounts of health. I will admit that this could be balanced better but this takes time.
In regards to the Mana Bar, I agree! In fact I have already increased the max amount by a factor of 2, and increased the regen speed slightly. I have also balanced the spell costs a little better.
If your Interested in trying again with the new balances there will be an update some time in the future (Probably after Judging ends).
Thanks for Trying it out!