I was torn between MK and EPCOT growing up. EPCOT (Center) had the edge, though. And it stayed with me as I got older, even as the park languished. It was the diversity between the parks. That they both represented WDW - but felt very different in tone and theme. Yet, everything still felt "Disney" in execution. I actually know a lot of people who said they didn't think they liked it as kids, but it quickly became their favorite park as an older teen and into adulthood.
When I started going in the 1990s, my family all preferred EPCOT over MK and MGM. As many have said, the big thing that is draining away from the parks is their distinctiveness from one another which was always a big part of the appeal. They are leaning into making Epcot aesthetically different from the other parks, but attraction wise it seems they're trying to push it and all the other parks toward being a collection of movie-based attractions behind different themed facades.
That said, I am a bit mixed on what direction EPCOT should have taken. I suspect that WoM would not have aged well even with updates, for example, and a greater mix of different types of attractions in Future World probably was needed. Some things they did should have made sense, particularly Test Track and Mission: Space which added some thrills, were ambitious attractions, and focussed on the kinds of themes that should have fit well into the park. While neither are bad attractions, they ended up as kind of mediocre and never really became popular enough to boost the park. If anything, it was only with Soarin' that they finally got Epcot a WDW 'must see' attraction (for many guests, anyway). Not sure where the blame lies for this, as the concepts make sense, at least to me.
Elsewhere, what they chose to keep, refurbish, and close is at times baffling. Beyond the big tragedy of Journey Into Imagination, it surprises me that Wonders of Life was shut down so promptly. It was a flexible, interactive space based on a theme of health and fitness that is still one of our main obsessions as a society. It just feels no-one really thought the implications of these kinds of decisions for the park beyond the immediate concerns of sponsorships, etc.
I'm sure both Guardians and Play! will be popular. Still, it is part of the phenomenon that makes it hard for me to get enthused about Epic Universe. That seems a perfect crystallisation of what all the parks in Orlando are becoming: movie-based lands and attractions gathered together under random, almost meaningless names.