I agree with what many have already said on this thread. DHS and Epcot seem to have the least coherent themes at this point.
MK is a deliberate mix-and-match of different genres, and I think it would be more accurate to say that the theming of specific lands in MK has suffered. Tomorrowland definitely lacks cohesion, although I'm sure it will look very different in 2021 than it does now (still, I think Tomorrowland needs more than the Tron Coaster). But overall, to me, MK's theme can be preserved as long as new attractions are themed to fit the individual lands. The issue at MK is a lack of new attractions in general, and the fact that some of the older attractions could use a serious update, or even replacement.
DAK is personally my least favorite park, but undeniably has the strongest theming IMO. I don't care about Avatar in the least (I'm not even neutral on the movie, I actively disliked it), but I don't have an issue with Pandora @ DAK. I think a mythical land (with mythical flora and fauna to explore) was always in the cards for DAK, and just got put on the back burner for so long many forgot about it.
DHS is just a mess. I may be in the minority here, but the loss of the Hollywood/Backlot studio theming @ DHS is much more upsetting to me than the loss of Epcot Center. I loved the GMR, Studio Backlot Tour and Animators Academy, and I'll be gutted when the park loop of classic film scores (My Fair Lady, Sound of Music, etc.) is changed out for something more thematically appropriate. But I've made my peace with this, and I'm just hoping TDO can find a theme that works for DHS going forward...I'm excited for individual lands and attractions, but have a hard time understanding how a Mickey Mouse ride, the Star Wars and Toy Story lands, RnR and the old Hollywood feel of Sunset Boulevard and ToT will have anything to do with each other even in the loosest sense...
As for Epcot...World Showcase is fine as is, but I have no idea what's going on with Future World. I approach IPs on a case-by-case basis, but I'm not too thrilled about GOTG (although IMO, Universe of Energy had to go). It's very sad walking through FW and seeing unused or underutilized pavilions. Again, I'm absolutely willing to part with Epcot Center if TDO demonstrates that they have a new plan with a clear theme in mind...I'm not convinced yet that this is the case. I'm hoping there will be more Epcot announcements soon, since a new restaurant, upgrade to Mission Space and GOTG attraction doesn't seem like enough to fix this problem.
Obviously DHS is the worst off at this point, but at least we all know that will no longer be true by 2019...The same can't really be said for Epcot yet.