I think it's simply differing interpretations of the word "varied". You're talking about the dungeon "type" (corridors, not multiple paths, a bit linear). Folks that find them to be varied are talking about asthetics, decor atmosphere, colors etc. You have to admit, in Oblivion and even more so in DA2 you walk in and find you are in EXACTLY THE SAME F****ING ROOM..............again.

(it actually didn't piss me off in DA2 because they don't impose much dungeon crawling/exploring on you. You're in you're out. That game is, in my opinion, more about relationships but that's just me).
So really, based on your criteria, I think you're actually "right" for what it's worth. But so are some other folks based on what they mean by "varied". I just think some folks are being stubborn (on both sides) and getting caught up in "right fighting" instead of at least trying to understand where the other is coming from.
Well, I haven't exactly hidden that I was complaining about the layout and not the aesthetics of the dungeons

And yes, I do agree with your anolysis, but again, it's not like I've ever said the opposite ; my point was just that such linearity removed all the fun that could have come from the better craft of the dungeons.
What surprise me is more that so many people seem to not mind this linearity (again, regardless of the visual aesthetics and hand-placed set pieces), here of all places. TES forums have usually a rather bad view of games like Call of Duty, which are basically the exact same kind of design that these dungeons (ultra-linear corridors with nice graphics and lots of "scenaristic" events), so I'm quite surprised to see such an acceptance of this very design being the core of the dungeons.
At the very least, I would have expected much more people UNDERSTANDING why ultra-linear dungeons can be supremely boring by their very linearity (and hence the lack of exploration), regardless of their visuals.