MK was always in the plan. That what was going to provide the income to do the EPCOT project. That is where most of the residents of EPCOT were envisioned to work. He made the decision to buy all that land so they could easily fit in what he wanted and keep it isolated, if necessary, from the rest of the world. Just because he wasn't able to actually see any of it through, does not negate the fact that none of the areas of Kissimmee or Orlando would be what it is today without one single person that had made a bigger impact on modern day life. Walt wasn't there to see it become the most popular vacation destination in the world, but he did build the foundation that it was built on and he did that while being dead for the last 55 years. What influence have we been directly responsible for in spite of being alive. The name of the place is Walt Disney World! Not Roy Disney World or Nine Old Men World.
I give Roy credit for going ahead with the plans for Magic Kingdom and being wise enough to know that the original Walt Disney idea for EPCOT was not going to fly and would have been such a drain on resources that it would likely break the back of the Walt Disney Co. I will agree that Roy does deserve a bit more recognition for that, but remember it was just about a month after MK opened that Roy, himself, passed away. Neither one of the brothers had a hand in what todays WDW has to offer.