The whole issue of crop sensors just doesn't ring true the way its discussed. It's as if a crop sensor just gives less.
I would like to offer the comment that "ALL' lenses give excess coverage. My 240mm symmar nearly covers 8x10 at infinity, yet it's rarely used that way. Why, well 8x10's are rare as hen's teeth compared to the 4x5 and secondly the lens changes in character as one focuses. The image circle enlarges as one focuses closer. So we're talking about surplus coverage. The 240 focused on a 8x10 at infinity suffers poor edges and light fall off. Sharpness is less than stellar at the edges(however on a contact print, its still #### good) as sharpness tends to fall off the further from the optical center. Pull the bellows out and the edges clean up nicely.
Using the same lens on a 4x5 is an entirely different issue, sharp edge to edge, plenty of coverage for tilt, shift etc. Its works well because we have "SURPLUS" quality (call it sharpness, resolution, contrast whatever). Using less than full coverage is common to all formats from mini to maxi. Therefore "all" cameras are crop camersa
Quality of a lens in most designs is a series of compromises, certainly cost being one of them and throughout history (mine anyway) we always expected lens quality/capability to fall off in the corners. The other corrolary is the center will be much sharper, in most HQ optics a "surplus" compared to the film/sensor( it took micro fine grain film to get a sense of ultimate resolution) so we were sensor (film) limited.
So as I read the MTF charts on teles and long normals, there is a nice distribution of lens quality, nearly out to the edge of the image circle. So if the lens has enough surplus to get all out of a sensor, what else is needed. Teles work fine for 35mmFF or DX with acceptable lens capability. Other factors dominate that part of the discussion, i.e. weight, aperture, etc.
Wides are another issue. High resolution 35mmFF are on the ragged edge as the sensors are now the limiting factor. It can be acceptable, but Canon doesn't currently have the solution and they are the only purveyer of FF cameras at present. Apparently Zeiss has a good design, at least from what I read, but now we're dealing with stop down metering, adaptors etc. Still it shows what can be done. All at great expense for the customer/fan of FF.
Smaller sensors with optimized lenses can equally/esentially work well. As long as the sensor and lens are designed to coexist well, an equally good solution is available. Wide angle 35mm lenses on Dx lose there wideness so DX lenses MUST be provided.
The point of all this is we are discussing issues already identified and solutions being worked on. It is not Canon (FF) vs Nikon (DX) & Canon (APS-C). Canon is in full frame, entirely due to marketing and image. The dollars generated are a drop in the sea compared to the vastness of their other enterprizes and formats. Pretty effective and many of you all are surely convinced.
Nikon has a more elegant solution from my perspective. High density sensors doing more are on the correct side of Moores Law not reducing the cost of silicon platters and chip yield.
In-camera processing is in it,s relative infancy and will make high density sensors much more capable going forward.
Some ask, why I have switched partys. I have been known to carry a brand C camera for 30+ years.
I like Nikon "Color" in the D2x. I prefer it over the competitors.
I had a ton of FD "L"'s that Canon obsoleted and I enjoy using older mf lenses. (I'm using 30yr old AIS Nikkors now)
The D2x has so much excess sharpness and enlargeablility that I wouldn't even concider a larger format camera at this point, that included FF35mm.
4x5 film still represents the ultimate in image quality at an affordable cost.
And DX will always provide acceptable quality at a lower lost or more features for the dollar.