It is also true you have to know what the rules are before you can even think about twisting or breaking them. I've been looking at common features of fairytales as part of the Future Learning Hans Christen Andersen online course I'm currently studying. While I think a lot of the language used in this kind of analysis is more convoluted than it needs to be, the features do make sense and you can see how one step leads to another and then another. From there of course the story quickly builds up.
I also think the Rule of Three principle is a natural way to tell stories. You do need Event 1, Event 2 repeated, then Event 3 where the situation changes or a problem is resolved. Without that middle repetition, there is no build up of tension yet equally you don't want endless repetitions. It becomes boring. Yet who first came up with this? It's a centuries old technique and is found in the Bible (see the Parable of the Good Samaritan - the priest, the Levite, the Good Samaritan. Three characters and three reactions to the situation). I'm reasonably certain the Rule goes back further than that and emerges from the oral tradition of storytelling.
So do writers despair there is "nothing new under the sun"? No. We use the rules to strengthen our stories and recognize readers need a familiar framework to follow. I think writers need them too.