[Snake]

If Spellthieves are supposed to be 'I can do everything without consequences' class, then Boxer should do insane damage for high FP cost again. Kensei should be impervious to basic hits with percentage basic hitting passives. Demon Hunter should be able to dodge whatever you toss at them, hit infinitely with skills, deflect bullets with katana and gun at the same time, reduce a chomp of 20 damage and retaliate with roars for unresistable damage.

Right?

Spellthieves are cancerous for the fact they'll always make any future additions related to magic their DLC, and bonus points if the magic is like, really good but limited to a certain class, but they can still use it uber efficiently, and sometimes better than the classes the magic belongs to anyway.

God rest Ranger's soul if their spells didn't require a Bow.

Now on to solution, and deviating the focus from the OP a little to solve ST's problem:

- Either make Copy Spells receive a big 8 round cooldown when used, or make them vanish on the first use.
- Negotiate should really be a skill that can be silenced by the Silence status, it's ass to fight something that removes your debuffs for FREE, not even a status inflict check.