Personally, I think AK really requires a full day, especially now with Pandora. It's a huge park with a lot to do, but because it is a THEME park rather than an AMUSEMENT park, it has always gotten an ill-deserved reputation as a half day park. People think "well, there aren't tons of rides, so not a lot to do". But, if you're interested in the wildlife trails and the rides and the shows, it has always been a full day park and now is more than ever because they have added two more rides.
Now, this is all very subjective, but I would probably dedicate 1 day to MK and 1 to AK, and then split your second day between DHS and Epcot and do the highlights of those parks. Book your FP+ reservations for whatever park you plan on doing in the afternoon. I feel that unless you really really want to see all of the countries in the World Showcase at Epcot, you can hit the highlights and be done pretty quickly. We like the world showcase, but touring mini, disneyfied versions of various nations might not be everyone's cup of tea as far as how to spend time on a very short visit.