I don't think that I or anyone else here ever said that the overall experience of shooting doesn't matter, for example there is a world of difference between the viewfinder experience of using a rangefinder camera, a digital point-and-shoot, and a high quality SLR. I understand that the experience you describe may seem compelling for you and others. But the idea that the simple visual comparison of one camera / lens viewfinder image to another camera / lens viewfinder image can produce valid data about lens equivalence is a misguided concept. It's a false assumption that translates to false conclusions.
Viewfinder image size is a complex subject. Viewfinder image size is affected not just by the lens, but also by viewfinder magnification and viewfinder crop. These are different for every model, not to mention the fact that you would have to find a way to actually measure objects in the viewfinder to generate repeatable data. You're basing your whole argument on "perceived distance", whatever that means. How do you measure that? You can't, because it's all based on "perception". It would be so much more straightforward, and more accurate, to just take a few pictures and compare them side-by-side. This has already been done.
The only reason I'm still debating though, is that after all the proof to the contrary, you still deny the basic fact and main point of contention that a 50mm lens on a 1.6x crop camera and an 80mm lens on a FF 35mm camera are essentially equivalent, in terms of framing/field of view, compression, and perspective distortion. Even in your last post you once again made the statement:
"I expect those 50mm and 80mm shots wouldn't look as identical as you're suggesting."
You could easily prove or disprove this by just setting up a tripod and taking those shots. I've not only done this exercise myself with several camera models, I already posted several links to where respected photographers have demonstrated it and proven the relationship to be true (not to mention that I've "shown my work" by explaining the math).
I'll give you that the experience you described about alternating between the naked eye and your viewfinder can be an interesting exercise, in a "gee, look at that" kind of way. What I can't agree with is that it carries any weight in determining whether a given lens is, in your words, "useful and intuitive" for any specific application. No photography book, class or professional I'm aware of has ever taught to use that particular "experience" as a basis for choosing the most appropriate lens.
In respect to this lens, we're talking about an 80mm equivalent focal length on any Rebel or 7D, which is not a particularly useful focal length, as it is too compressed to be used for most indoor photo opportunities, and not long enough to serve as a good facial portrait lens. Never mind the fact that it may happen to display images in some viewfinders at close to real-life size; that alone is no basis to recommend this as an appropriate first prime lens for 1/6x crop camera owners -- it's more of a coincidence than anything else.
There's a reason that Canon and other manufacturers chose certain focal lengths that have stood the test of time: The 50mm is the standard, all-purpose lens and for many people the only lens they ever bought, for the very fact that it was the most "useful and intuitive".
I believe a beginning photographer with a 1.6x camera would be much better served choosing something like a 30mm lens as their first prime, which provides a view most similar to the full-frame 50mm. Yes, those are respectively what are known as "normal" lenses, and one reason they are called "normal" is that everyone going back 150 years decided that the ~53 degree angle of view is a "natural" view that is neither too expanded or too contracted. In other words, the "normal" lens is the one that most photographers long ago agreed is the most useful and intuitive -- certainly not 80mm or its equivalent, and many pros are now of the opinion that an even wider lens, such as a 35mm lens (21mm on the 1.6x) more closely simulates the human field of view.
For those reasons that I don't think most crop camera users would find the 50 all that useful, and in my opinion the 50 is better suited for the full-frame format for which it was originally designed and intended. I've used the 50 on my 60D for some product shots and a couple times outdoors, but mostly it stays on my FF camera.
You wrote a very thorough and popular review, with only that one small line that caused all the hoopla. Like SkunkWorks, I guess I just want everyone reading this to have all the facts before buying. Besides, I enjoy a good debate! Thanks and best wishes.