We talk about these issues like we really know whether most movie IP draws people in, but do we really know whether it does or not? And does Bob Iger, for that matter? It's not clear to me that Avatar is drawing people in because it's Avatar, or that people really want to be immersed in Remy's Ratatouille world or whatever. For my kids, with the exception of a few movies they like, they really don't care whether the ride is themed to a movie or not, and a lot of times they just say "who's that?" when some strange character appears (like the Michelin man guy from Big Hero 6, which they've never seen).
Now, I can certainly accept that the situation is different for other people who want to see Radiator Springs, etc. But I think there's very little way of directly measuring, for instance, whether Expedition Everest would be 24% more popular if it had Moana grabbing you at the top of the mountain or whatever. We can speculate based on our own preferences, but that's about it.
I'm skeptical that Iger really cares about that angle, anyway, despite his response here. I think it's more about promoting the films and selling merchandise rather than making the parks immersive.