Then there's the fact that while Disney was pouring a Billion bucks and all their heart into Epcot in the early 1980's, they were simultaneously planning and paying for a complete overhaul of Disneyland's aging Fantasyland. And that New Fantasyland that opened in spring 1983, about nine months after Epcot Center opened in October '82, was a full reskin and re-Imagineering, leaving nothing in the land untouched (except Matterhorn and Small World, which were physically removed from the land proper and already darn good rides).
You could use the 1.2 Billion dollar extreme makeover of DCA from 2009-12, with the opening of the fabulous Cars Land in June '12, as an excuse why they are stretched too thin there in Imagineering.
But thirty years ago they accomplished an even bigger feat by building Epcot in '82, plus a little thing called Tokyo Disneyland in '82, plus a full remake of Fantasyland for Disneyland in '83. And that was before all this new technology that allows for instant global communication from anywhere, and superfast computing and engineering, and a more developed contractor network for the themed entertainment industry.