Black Mage needs a buff to allow casting while Moving.

[Jezvin]

That would be why you call it Void Focus or something and it makes you just float on Aether so you are not actually moving around, You are standing casting but the magic is lifting and moving you while standing.

I don't think instant cast is the right answer either, it takes away from the spell casting aspect of the class. Standing there for a few seconds charging a massive damage spell is very satisfying.