Universal's ad slogan used to be "ride the movies", their very first tourist attraction was a tram ride through their Hollywood Backlot, years before any formal park was built. Their whole gimmick from day one was simulating scenes from movies and explaining how that was done. The only changes have been the inclusion of movies not made by Universal, such as Harry Potter, and not focusing on the "how to" side.
Disney used to treat attractions as their own creative medium to explore. The golden age of Imagineering from the early 60s to the early 80s saw them consistently take this approach, which was still sometimes continued in WDW until the opening of Expedition Everest. While some non-IP attractions have been built overseas in the past decade (such as Mystic Manor), in the states Disney has completely abandoned this kind of thinking with only minor exceptions like Awesome Planet. In a number of cases these IP rides have been made on the cheap, with the thinking that the brand association would make up for any shortcomings in quality.
Universal's approach to attraction design had a built in shelf life. The soundstage look of the park was intentional. Don't spend a lot on exterior scenery because what's inside will be gone within 10 years. That obvious lack of quality is what set Disney apart. They built beautiful, timeless attractions that lasted for generations and did not chase fads. When Disney blatantly tried to copy Universal with MGM Studios and its cast of current movie and TV characters, the results did not match the attendance of Magic Kingdom and the shows became stale within a few years.
What Harry Potter did was to show Universal what the public really responded; beautiful design. No more beige boxes with a "Harry Potter" marquee. The attraction looked like Old Europe and was far and above anything else at the resort. Universal has responded by committing to a new third park with this level of quality. That represents and improvement for them from their humble beginnings, but the park will still by tied to IP that may date itself over time, or already be past its prime (Fantastic Beasts).
Just like in the mid-80s when MGM Studios was first announced, Disney is now trying to copy Universal. Avatar and Star Wars are so obvious attempts to recreate that Harry Potter magic that even the general public has noticed. Now Disney is being compared to Universal and not always in a positive way like it used to.
We as Disney fans don't want to see WDW become an imitation of Universal. Whether that's the Universal of 1990 or 2010, the WDW parks need something substantial to differentiate the experience or else all Orlando parks are just going to become more or less the same thing with the only difference being the movie the ride is based on (keep in mind now BOTH parks are using IPs not originated in house).
IP is tolerated at Universal because it's been their sole focus from day one and their attraction design approach has improved over time. There are exceptions like Fast and Furious, but that's been the trend for the last decade. We like seeing Universal do better.
Disney has almost completely abandoned their approach of treating attractions as their own creative medium, something WED realized and wanted to pursue once Disneyland was a financial success. Disneyland's use of IP in the beginning was to help compensate for the lack of funds to build quality attractions and some of those (like the 20,000 Leagues set tour) were scrapped before Walt passed away. The E-tickets that made Disney famous like Space Mountain and Haunted Mansion are no longer appreciated by current leadership, even though people still line up for them decades after opening. We want Disney to do better and build better, and not just rely on the crutch of IP to justify everything they do. We became Disney fans because they saw the potential in a blank canvas, not because the parks looked like a version Universal Studios with Disney movies.
