Thanks for the fairly comprehensive and reasoned response @PinkElephant!
Of course, I can see all that on one level. But, as an Evernote customer wanting the best user experience wherever I use it, the Android desktop mode via Dex falls well short of that. And it is extremely frustrating when I have as much or more power and storage in my phone as a lot of people have in their laptops. At least if the UX becomes more consistent across Android / Android over Dex / Windows that would be some improvement.
Even so, I assume that Evernote has very impressive developer resource to call on and being ahead of the curve in implementing Dex / Android desktop mode might actually prove to be a good thing.
The one small grain of comfort I take from this is that Apple users are no better served that us Android users - because if that happens I'll be gone!