You don't need a popular or strong IP to have a great attraction. You just need a well designed/engineered attraction. The Lost Continent pre-Potter was my favorite theme park land and it had nothing to do with an IP. It was well themed and had great rides. Also, I'll reiterate the example that's always used in this argument: WaterWorld at USH. Considered a not-good movie, and a movie the majority of people have never even seen, but people love the show. So again, if they do well with a theme, they succeed. And horror is fail-proof... if they do it right.
Also, as a side note, a permanent theme-park land and a temporary HHN house are two hugely different beasts where IPs are handled very differently.