I don't consider a misfocused shot to have better image quality than a properly focused shot. There's more to capturing an image than the sensor (and the difference between the image sensors is less than the difference between the AF sensors).Neither do I. But the 6D is more than a sensor, and its AF is superior to the 5D2's, which sold for a $1k higher price than the 6D has sold for during most of its initial year on the market. Therefore the 6D is a fantastic camera for the price, period.
I was comparing two contemporary cameras, the 5DIII and 6D, not a 5-year old camera that has been replaced. But yes, the 6D is a fantastic camera, for it's price. My Subaru is a fantastic car for its price, as well. It can go through over a foot of snow on the driveway, with drifts as high as the hood of the car, if I need to get out before the plow service comes. It even has heated seats to keep my butt warm. But a well-equipped Volvo (5DIII) would be better, and a well equipped Mercedes (1D X) would be better still. The point is, while the Subaru meets my needs as a car, the 6D does not meet my needs as a camera.
The price of the 5D3 is mostly the difference between the AF sensors, and a good bit of faster/more processing...and a whopping 1.5 frames per second of extra multi-shooting. But like it or not, in most situations you simply have to try to upset the 6D's AF sensor to make it misbehave...which is something you might take pleasure in...in order to goad 6D users...but owners of this camera are happy to work around its shortcomings...and we get fantastic images doing so...most of which are in focus. Sorry to burst your bubble, but it can only grow so big before it pops.
increase in frame rate (plus a more durable shutter) and a much
better AF sensor are significant improvements. "Try to upset the 6D's AF sensor to make it misbehave?" Yes, how dare I try to take images of running children and expect good tracking? My 5DII couldn't do it very well, and despite it's 'AF superior to the 5D2', the 6D isn't really any better at it. I don't think that upsets the 6D's AF nearly as much as complaints about the 6D upset you.
I have to ask though, do you own a 5D3? If you like it so much, you really should buy one, and sell that crappy 7D of yours. It's not like the cost is going to set you back that much. You already own the 1DX, so I have to wonder why you are so in favor of the 5D3, when you didn't even feel the need to buy one for yourself?
No, I don't own a 5DIII, although I've used one. Since we're talking about AF, the 5DIII is very relevant, since it has the same AF sensor as the 1D X, and it's more affordable which as you know is an important consideration for many people. I sold my 7D quite some time ago, it doesn't offer any advantages over the 1D X, for me. But it was a very good camera. A year ago, calling the 7D 'crappy' on this forum was sure to draw out a response from the staunch defenders of 7D awesomeness. Those folks are quiet these days, but their spirit lives on in the staunch defender (or defenders, if there's more than one) of the 6D.
I see no need to buy a 5DIII, as I have no plans to carry two cameras around routinely, and the EOS M is more convenient as an emergency backup. Since I prefer a gripped body, and the gripped 5DIII is larger, heavier, and less comfortable to hold than the 1D X, if I absolutely needed a second body, I'd get a second 1D X. But the 5DIII is an excellent camera, great IQ and
great AF performance.