[Fern]

Locking Spellthief out of support spells not only makes the class a lot more unattractive, but also throws it at the "weak rogue promotion" club. The only reason why Spellthief is related to the issue is because you can mix DK, Malmelo and Sanctuary together- the rest of the stolen spells they can do, but slightly worse compared to the original class since it doesn't have the same skills that support it as the original (ex: Annorum, Hexer curses, Detailed Care, etc.)

Even if you blocked them from using support spells, it wouldn't change the core issues that are DK/Malmelo/Sanctuary. People could just change to Kensei/Hexer and stack multipliers over and over still, could be able to run Priest solely for Malmelo and Sanctuary as well.

"Don't search for the cat's fifth paw."

(yes that's a saying in my land-)