Problem: Everything that matters is immune to enfeebles.
Suggestion: Job Ability for one cast that ignores immunities.
JA: Overcome
"Allows your next enfeebling magic spell to overcome resistance."
Recast: 15 min.
Basically, all it does is remove the little checkmark that says it's immune to the debuff, so that your spell either goes through or resisted like any other enfeeble. It does not mean 100% success.
Would this be too powerful?