I think this is akin to the "donkey's left eye" argument. There's a story where you'll be given a million dollars as long as you never think about a donkey's left eye. It's certainly something you'd never give a moment's thought to before, but the second it's brought to your attention, its
all you can think about.
I've been to Epcot many times over the years, and I've never once noticed the Soarin building like that. Now that you've shown me that pic, I'll probably notice it now, sure. But prior, it's totally escaped me. Probably because the go away blue/green did its job, and I choose to focus elsewhere.
These designers sometimes make deliberate choices to draw you eye to certain areas. I know it's been suggested that the unfinished/studio sides of SLOP be outfitted with at least brickwork, but if they did, I think it could possibly distract the eye
to it, rather than to the facade right in front of you.
In the Soarin example you give, I wonder what you'd suggest they do with it. If you did say make it a building or mountain, I'd argue that it would draw the eye from the other building already there, which is where they want the attention.
Take a look at this pic of TDS.
The giant speakers on the poles dominate the picture. They're not themed at all, and totally stand out. There are ways to hide speakers. Why didn't they? Do you notice them more now that they've been brought to your attention?
Point is, if you look hard enough, nothing is themed 100%. Theme park designers are interested in illusion and drawing focus. It's not about theming every square inch, it's about theming every square inch that matters.