I think the big issue a lot of us have with Disney's insistence on IP-based attractions is timelessness. McCarthy claims the desire to use IP "that really resonate(s) with our customers." But if there's one constant in pop culture, it's that it's ever-changing. It's human nature that as a collective, we all get tired of thing and move on to other thing. While it's true that some IP can transcend this, the vast majority of it cannot. What resonates now is not what resonates ten years from now, and by-and-large, you want theme park rides to last more than ten years.
So, long-term, with a plan like this, you just wind up with a multitude of dated attractions and not enough desire/cash to replace them with something new because there are so many of them. A good example is Uni's Revenge of the Mummy. Despite their efforts to reboot that franchise, the ride's theme is horrifically outdated, despite the quality of the ride itself. Versus something like Everest, which remains a titan in amusement ride storytelling that pulls in consistent lines, acts as a highlight to plenty of vacations, and retains a modern feeling despite being over 15 years old without any connection to IP.
So, sure, if you flood the parks with, say, Guardians of the Galaxy right now, that's a good decision in the short-term because people are going to want to book trips specifically for the Guardians of the Galaxy ride. Vol 3 just released, and James Gunn signaled that we won't be seeing those characters as a team again. How long before those rides are tacky relics of a time long past? I'd bet serious money that when that happens, Everest is still pulling in enthusiastic crowds.