The ponies using them have limits. The Elements, so far, do not. But, with any greater threat not to be defeated by the Elements, you will need to work out just why they can't this time. A problem that wouldn't exist if they just can't use them.In fact, it begs the question why they couldn't before anyway. Wasn't the movie set before the end of season 7? Why not use them against the Storm King? I just fear there will be lots of hoof-waving in the future.