I have cleared those fights as a WHM/AST pair as well, and I've used CU at a number of different points, but what pisses me off is that the change was utterly unnecessary; the move wasn't particularly OP, given the limitation that you cannot do anything else at all while it's up and need to stand in the thick of things, and it in no way conferred any undue advantage to AST over WHM or SCH. Each one continues to bring unique strengths and weaknesses. Instead, all this does is diminish the utility of an already selective use spell, especially if what I've seen people report about heavy damage interrupting it too is the case! (I cannot confirm this myself, having not yet put that to the test)

Even if being interrupted before the bulk of the damage goes out is relatively rare, that doesn't mean it doesn't happen.