Oh, multiclassing is going to be hilariously broken on release. Even besides the baffling comment about fireball, there are so many specific rules about how different class features are supposed to work with each other that there's no way they've implemented it all (correctly), especially since they seem to look at dnd rules a little contemptuously, like they're more of this "stuffy old inconvenience" than something that exists for a reason.
E.g. I'm almost expecting saving throw proficiencies and extra attacks to stack.
