I don't know. Many restriction for classes only exist because otherwise they can't be balanced. Mages can't wear armor, because they just would be to powerful in D&D. They can wear armor in Beyond Divinity though, which is classless.
I fail to see why restricting characters to what there class is allowed to use is better, although some warrior skills that that are a bit more inventive than what there is now, would be a nice addition.
