Harry Potter really isn't orginal in terms of story, but in terms of setting. Boy is orphan raised by aunt and uncle.
Boy feels alone and wants something more.
Boy gets message that leads him to a wondrous place.
Boy finds out he has powers and great things are expected from him.
Boy gets training for coming war where he will be a hero.
Boy defeats great evil from his past.
Boy is hero. That's Harry Potter, or Star Wars, or any of a hundred other stories. Harry Potter is unique because of setting and richness of character development, and though it may be derivative, it's not pap. It's a story we want to be told again and again because we all want to be Harry Potter or Luke Skywalker.
Because structure is a commonality across all drama. Despite what pedants think, nearly all Western narrative consists of a beginning, a middle and an end. Audiences enjoy seeing character growth. The fundamental cycles of the monomyth, Campbell aside, can be found in a plurality of stories and legends across cultures. Psychologically speaking, we like to have certain elements in our storytelling. Alexander Polti divided all possible works of fiction into 36 dramatic situations and when you look at it like that, everything is "derivative" of whatever came first, whether or not the author is even aware of prior works. It has been argued that The Hunger Games is "derivative" of Battle Royale but this argument is largely made by people who want to hate on Suzanne Collins. The fact of the matter is, both stories deal with schoolchildren made to fight on television. Collins had a much different message to convey, however, and although the scenario is the same the denouement and plot are very different. Besides which, Suzanne Collins was unaware of Battle Royale until Hunger Games was finished, so if the definition of "derivative" includes derivation, Hunger Games ain't. Both stories owe an awful lot to Walter Moudy's "The Survivor" but dollars to donuts neither one of them had ever heard of it. As a part of the collective unconscious, maybe - but then, all three stories owe their existence to Fredric Brown's "Arena" which most people know from this: Now - is Hunger Games derivative of Kirk v. Gorn? NO. But they definitely have elements in common. Wanna see derivative? This is derivative:
If you want to be that hyperbolic you could say that writing letters to make words is not an original invention. We're talking about major story elements here which play out across a ton of stories. I think that's derivative. You don't and you've made your point well. I guess I enjoy derivative work equally alongside original work. If Harry Potter is telling the same story as Star Wars it doesn't matter to me. Both were fun to watch though I prefer Star Wars.
I answered that question succinctly with Star Wars. You said that it was guarded from guilt of derivation under the protective category of the monomyth. I disagree with your argument as too broad and told you as much. If you'd like to have another try at explaining why stories which are as similar as Star Wars and Harry Potter are not derivative of the former as the former is derivative of many stories which came before it you are welcome to it, but your tone is rude and doesn't help you in any way.