Sounds more like back-pedalling through moving goal posts to me
Not at all. You can't just say that full frame is "better" merely because it's a larger format. By that argument, a Phase One MF system is "better" still. I have access to one of those, with a IQ180 back pretty much any time I like. I rarely use that opportunity though. It's sharper than a 35mm camera, so surely it's "better" right?

Surely I'm an idiot for not shooting everything on a £20,000 camera... it must be "better". LOL
I've not even looked at your two comparison pictures. It's pointless. Just as pointless as if I was to post a few images where the differences between formats was obvious. All that would prove is how easy it is to hoodwink with highly selective examples.
Up to a certain size, yes it is.. which is my point. If yo regularly print big, you really do need a full frame camera (assuming you know what you're doing with it). Unless you hadn't realised, I'm advocating that the best camera is the one best suited to the job you are doing.
On this comment though: "Most people only want a full frame camera because they just want to own one, They don't have a need for it. They use inappropriate lenses, and use it inappropriately. There's only an advantage to full frame if you know how to get the most from it, otherwise the differences are pretty limited..."
What's wrong with just wanting something? Choosing it, owning it, and enjoying using it is all perfectly valid IMHO. So what if they don't get the most from it, and who are you to judge anyway?
There's nothing wrong with that. However... just don't start expecting miracles from the gear is all. Having a full frame camera won't make your images any better. Use a tripod, or keep the speeds up... and use sympathetic apertures, and yes they'll be sharper. Usually though, you'd probably not notice much difference. In fact, how many times in here have we read about people not being happy after upgrading? A more exacting tool requires more skill to wield it.
You often say the difference between full-frame and APS-C is only visible in large prints (which ignores changes on DoF, dynamic range and noise)
It doesn't ignore that at all. Noise for example is only relative. You can't look at a print and judge what it was shot with by how noisy it is. You could be looking at a shot from a full frame camera at ISO6400 or a shot from a crop sensor camera at ISO3200. You'd never know unless you compared side by side. Same with DOF. It could be a shot from a full frame camera with a 50mm lens at f2.8, or a shot from a crop sensor camera with a 35mm lens at f1.8. You'd never know. As for dynamic range.... it's a total red herring. A Nikon D7100 has a wider dynamic range than a Canon 5D MkIII.. by almost 2 stops, so can we stop talking crap about DR please?
but this overlooks the modern way of on-screen working. We don't make so many prints these days (which is a damn shame, though a different topic) but what we all do is hit that 100% button, and then the sharpness and other benefits of full-frame are easy to see. And that's that - it's set in stone.
But no one else sees that. If you want to show the images to anyone else... you'll be doing so at best on a 8MP screen, and usually on a 2MP screen... and usually a very small one, by showing the entire image, not a small section at 100%. If all you do is sit by yourself at a screen scrolling around your images at 100% then fine, but seriously, how pathetic an individual must you be in order to do that? You'd do it once to check sharpness, or you'd be that zoomed in to retouch. You don't "look" at your images at 100% though unless you print them big.
Back to my original point, and your statement:
"The image is all that counts." Not true, even if we wanted it to be. It's no more true than saying owning a car is purely about transport and getting from A-to-B - especially if it happens to be an American muscle car. (Big

from me on that score though

)
Of course that's all that matters ultimately. Ultimately... that's what people see as the result of your efforts. An image. Everything else is BS. All anyone else is ever going to see, and therefore judge you by is the image. The end. No one will give a hot steaming turd about this thread in a few weeks time, but everyone, always will be judging your images, and they'll not give a stuff what it was shot on. If you don't realise that, then you're not a photographer... you're just a gear nerd playing with his toys.
""ROB saying that crop sensor cameras are "great for snap shots and posting online".. which is clearly a load of crap."
Full frame cameras are also great for snap shots and posting online. If you genuinely believe that crop cameras aren't good for that then maybe you are ready to conceed that full frame is better!!
That didn't even make sense.