Thank you for playing the game!
I agree that currently the difficulty curve is too steep. Most enemy types and the enemy spawning system were added near the deadline so I didn't have much time to tweak the scaling and progression. As you said, the big ones should drfinietly have less health or I also thought of making thrm move slower.
The idea of new spells that help counter a certain type of enemy is certainly something worth looking into.
Very glad you liked the game and I appreciate the feedback!