Comparing the door to the wall behind it, yeah, I would in casual discussion say the wall is light gray and the door is dark gray. We can get pedantic and debate how far below photographic middle gray these doors are and if that still allows them to be classified as lighter shadows or darker midtones. But I fail to see how that advances the discussion.
It makes quite a difference to the discussion. There's a huge difference between pushing near-blacks to deep shadows with detail, and pushing near-blacks to midtones. Going from Zone II to Zone III or Zone IV is no big deal. Going from Zone II to Zone VI, which is basically what you've done, is quite extreme.
The simple fact remains that due to dynamic range limitations these doors were not able to be rendered properly in a single exposure by a Canon sensor. This illustrates my point which is there are real world scenarios when a Canon sensor is limited where an Exmor sensor would not be.
Maybe I'm worng, but I'm pretty sure I'd still take the two exposures with the Nikon -- if I was going for the rendering you went after. I'm pretty sure I'd only need the one exposure with either camera for the rendering I'd instinctively gravitate towards, though I generally always bracket just for the insurance.
Do you really believe the image would still be "respectable" with the pattern noise?
Of course not -- but how much noise is going to be visible is going to depend on how big the image will be used. I doubt any noise would show up in a 17" x 19" print, and I'm sure it wouldn't in an 8" x 10" print. And I have a hard time imagining anybody wanting this image bigger than that. Not for its artistic or technical reasons, of course...it's just that it's a prison cellblock....
Or that the doors should just be allowed to stay a murky almost-black tone? I'm pretty sure my client would not have been happy with those results.
Now we're talking about artistic interpretation, which depends a great deal on the particular client and the purpose.
If this was for a portfolio or marketing materials for the architect, your rendition is perfect.
But if it was for any form of reportage, I'd say you overdid the HDR by making the whole scene perfectly evenly lit. From your other descriptions, the attached image is closer to how I think the scene would have appeared to somebody standing at the camera position. I'm pretty sure that National Geographic, for example, would reject your rendition in favor of one closer to the one below.
(And, again, the architect would love yours and hate this one.)