[Chaos]

If copy spells were only usable once per battle, Spellthief would need a massive overhaul. As it is, its only used as a magic goodie bag, along with Distortion and Create Shade, because no one wants to break their weapon and lose all of their stolen spells on mediocre attacks, and if someone actually wants to attack with a dagger, VA is a far superior choice.

DK should definitely have its stat bonus nerfed, since Fallcall already puts it above the self-Shine Knighting skill, and IMO class skills should be stronger than item potentials.

Malmelo should be changed to be some combination of a flat value alongside a percentage of Light ATK, both increased by rank. Mercalan healing in the game scales off of SWA+Light ATK, but the possible SWA that could be used to keep the skill balanced would be so small that it'd be simpler to just give it a floor instead. I also think that using Light ATK in place of Faith rewards people who build Will and use sources that specifically give Light ATK over Faith.

If copy spells were once per battle, Final Flare/Hot Potato would see use. There is more to the class than Spell Snatch/Distortion/Create Shade/Mysterious/Negotiate, and while Negotiate is a cause for concern (See: Splash + Negotiate, for one), we're gonna have to see more of the class in action before Spellthief suddenly needs any sort of overhaul.

If we're going to make Malmelo scale, it should be off of Scaled FAI/2 at best, not Light ATK, and any flat bonus it receives should be very minor, as in +0.5 ~ +1 per Rank. We should not reward Elemental ATK stackers with the most powerful healing spell in the game, especially when you can use it without being a Priest.

DK getting a stat boost nerf would be for the best, yes.