This is true...BUT the difference here is that those Disney attractions are based on Disney movies. Their property. So it does make sense for a Disney park to include a Disney themed attraction based on a Disney movie, regardless of how popular or unpopular that film may be. While people here might not care for particular attractions at Disney, I've yet to see anyone say "that attraction based on a Disney film just doesn't belong in a Disney park."
I love how you start out saying that opinions are not facts (which I wholeheartedly agree with) and then go on to say how most children aren't really into dragons, unicorns, etc...as if that were a fact you were pointing out. Ironic, no?

Actually I know plenty of children who are (and for something supposedly so unpopular as dragons and unicorns, it's curious why both were used in Harry Potter). And to use your own argument, if you haven't experienced something like Beastly Kingdom, as it hasn't existed at Disney, how would you know it would be boring or unoriginal? Surely that's not fair? You really shouldn't judge something until you've tried it out.