On these two statements:
The original vision for the park has changed because in practice it didn't really work. (Otherwise, World of Motion, Horizons, Journey Into Imagination, kitchen Kabaret, The Living Seas, et. al. would have stood the test of time that other attractions older than them have (like It's a Small World, Pirates of the Caribbean or the Jungle Cruise).
The Living Seas was modified to include Findng Nemo because that dramatic, Sci-Fi vision of the seas became outdated and unpopular. As a theme park, Epcot's first goal (it even lists it in this order in the 1982 dedication) is to entertain. I am absolutely in favor of educating people in Epcot (future teacher here), but it must be done in an approachable and entertaining way. Not many people associate with the seas in a dramatic or science fiction-inspired way anymore I guess; what was good in 1986 isn't in anymore in the 2000s. Disney didn't close the pavilion's attractions for no reason; they closed one by one because the cost of running the attraction was no longer outweighed by its popularity. (The same thing happened to each of Future World's attractions one by one.) It doesn't make sense to run an attraction most people don't care to see. Disney updated the ride to make it resonate with today's audience and in doing so revitalized a stale part of Epcot. Today, The Seas with Nemo and Friends packs them in dail. Could the pavilion be a bit more informative? Sure it could, but the groundwork is there.
The funny thing about learning is that you learn more when you don't realize you're learning. It's why lecture-based classes are often tedious while active, discussion or project-based classes are often more interesting and informative. This is the path Epcot seems to be taking lately. (Nemo in The Seas, SSE touch screens, etc.) Yes, WDI needs to work a bit on their execution, but it all falls in line with Epcot's goal of "entertain, infom and inspire." The interests and expectations of the American and worldwide public are changing; there is no reason why Disney should attempt to entertain and inform people using tired methods that no longer apply to society. (Perhaps the rampant displeasure with recent Epcot is more a commentary on a common displeasure with society as a whole than a displeasure with Epcot alone?)