Oh, one other thing that I do think qualifies Frozen as being a shark jump (even with the “it fits!” qualifier from my first post). The arc of S4A largely focused (almost exclusively) on the Frozen gang. They were not guest stars who only appeared when the main cast needed them to, but they more or less took over the show. Almost every centric had then worked in somehow, something OUAT has never done before. Every scene with the exception of the long arching Author search was tied to Frozen and what the Frozen crew needed.
It’s like bringing on a really cute kid and making every episode about that cute kid and their antics, taking time away from the other characters. (Looking at you Cosby show, when they introduced Olivia to the character line up).