Hi! Thanks for playing, and for passing along feedback.
You're not the first person to struggle with spell shields - a lot of players find them challenging. That said, you certainly can get through them and beat the game.
Some small bits of advice:
1) Target shield casters before they can shield their allies.
2) Never let a shield-caster escape - they will absolutely ruin your day when they return as veterans.
3) Applying a status to an enemy will remove a stack of spell shield
4) Multi-hit attacks are a great way to melt through shields fast
Hope that helps you out a bit. Good luck!