It doesnt change that a Runeforge has to be weighed against 2 talents at that point if GA applying razorice isnt a bug.
But I might get on the PTR. Even without KM rank 2 you can get a good idea of what Obliterate would do with it, You basically just take the base damage and double it as long as the tooltip includes Might of the Frozen Waste. It can at least give you an idea even if it doesnt tell the whole story.