Actually, it was specifically the failures of Celebration that led me to think that EPCOT wouldn't have worked long term either.
While it's easy to draw the comparison to an HOA, EPCOT could have potentially been far worse: Reedy Creek and Bay Lake are controlled by a cadre of Resident Employees are they not? So the question would be, to what degree would potential EPCOT residents have been willing to give up personal freedoms and voting privileges to live there? Far beyond what just an HOA would manage, would they been allowed to elect a school board? A city council? A mayor? Would they be able to override Walt if they so desired? Would Walt have had sole authority to make deals to relocate corporations to EPCOT or would the citizens have some say in which companies would be invited/allowed into the town?
I think there are a lot of questions about Walt's EPCOT best left unanswered.
What failures of Celebration? People still live there and they‘re not holdouts living amongst blight and abandoned properties. The Walt Disney Company still owns The Celebration Company which continues to expand the development, although now it is done more through third parties. Island Village will add more than 1,000 new homes and an elementary school. Is it because Disney got out of the homeowner’s association early? That was always going to happen. Is it because Disney sold the Town Center properties? That, and getting out of the homeowner‘s association, occurred at a time when Disney was divesting a lot of property in Florida including some sizable chunks of Walt Disney World. Does that mean Walt Disney World is a failure? Like most New Urbanist developments, Celebration has failed to be a true live-work community but EPCOT accounted for that by being larger, having greater urban density at its core, being transit oriented and requiring residents to work at Disney World.
You seem to be under the pervasive, but incorrect, assumption that the Reedy Creek Improvement District has far greater power and autonomy than it actually possesses. The District‘s power is almost entirely focused on water management, land management and utilities. The District though is still bound by county (except those it is granted) and state laws and regulations. We know of new projects because they get submitted to the South Florida Water Management District for approval. The EPCOT Building Code cannot be less restrictive than the Florida Building Code. Reedy Creek Emergency Services enforces the Florida Fire Prevention Code. Disney pays county property taxes, and collects local and state sales and hotel taxes.
The District does not have the power to operate its own schools, so the residents of EPCOT would be voting residents of Orange County Public Schools. Disney themselves could have operated schools but they would have been private schools just like any other; local residents don’t have any say in how a Catholic diocese runs its schools. I can’t speak to the situation in the late 1960s, but for several decades now Florida counties have required major land developers to provide public schools in some manner. The Celebration School wasn’t just a crazy Eisner idea, it was a requirement for developing Celebration and is the property of the School District of Osceola County. Celebration High School and the previously mentioned new elementary school are also part of these requirements. So if residents didn’t want to use the private Disney school and didn’t want to deal with bussing to nearby Orange County schools, they could have pushed for the county and or school district to use their own power of eminent domain to build one within Disney World or even EPCOT proper.
While the Reedy Creek Improvement District is incorporated in the cities of Bay Lake and Lake Buena Vista, they don’t do much and the District still has power to act within a municipality. Even then, many major developments like Celebration or The Villages or Columbia, MD are unincorporated communities. They don’t have a city council or a mayor.
If you live in an apartment building that also has commercial space you generally have no say in the leases of that space. The reason residents of a city can typically stop a company from moving to a city is because there is usually a deal with the local government itself be it to buy land at reduced prices, tax breaks, subsidies, or whatever. The residents of a city couldn’t really stop a company from buying an office building and moving into it. So of course Disney would control the invited companies because they would be the landlord and the private entity providing any incentives. The big loss of control would have been over zoning, which can get heated, but again, there are plenty of large scale developments where development is effectively controlled by the developer.
A lot of the “questions“ about EPCOT arent actually something has not or is not being done right now somewhere. The Villages about an hour north of Walt Disney World is a pretty big example of a place with a lot of developer control that people have flocked to and continues to grow.