Prime Junta
I see that you've disagreed with me, so let me provide an example:
Here's Rostov's work from his artstation. There's a lot, so I'll just post one image I think that is most representative of DE's art style:
Looking along my subscriptions, here's Serhii Kasianchuk, who is neither an art director, nor even a prominent artist in the industry, as far as I'm aware
Here's Peter Polach (mild nsfw):
Here's Alexandre Chaudret, who is a director himself:
Borislav Mitkov, a freelancer:
Sergey Kolesov, who did some concept stuff for the Dishonored series, but (I think) was just a freelancer
Scott Gadile, freelancer
Jarek Kubicki, freelancer
Kayurova, freelancer:
Give any of these people free reign, and they'll bang out a user interface that will be every bit as splendid as the one in DE.
Long story short: DE looks good because artists set the direction, not because they had qualities that were light years ahead of everyone else