The 6D further improved on the 5D2, yet you don't give it any respect. You're biased, that's all.
Sure, it further improved the IQ a bit, which was already excellent on the 5DII. It improved the metering, too. It didn't significantly improve the AF or frame rate, which were the 5DII's biggest deficits. The 6D has a less robust shutter with a 1-stop lower max speed, slower Xsync, and a shorter rated lifespan. The 6D has a substantially longer shutter lag. So considering IQ only, the 6D improved on the 5DII, but overall it's a mixed bag. The 5DIII improved on the 5DII in pretty much every way. At least on Amazon (not that it means much) the 5DIII is outselling the 6D.
The 6D's biggest 'feature' is its lower cost.
Of course, AvTvM might say the 6D is not 'dated' because it has WiFi. Nice if you want to upload your JPGs to Facebook on the fly, I suppose. I thought it would be great for remote triggering, but someone pointed out that after a short time the connection drops, and you have to physically access the 6D to reactivate the link - that severely limits the utility, IMO (the WFT options for other bodies aren't limited in that way, but you pay a big premium for them).
* 5D III = 5D IIN
* 6D = 5D II v1.1
6D basically is a FF digital rebel to me. Marekting crippled product with a reasonable sensor and Wifi. About equally bad as Nikon D610, but better than D600, since it did not do splatter movies with its mirror. :-)
You certainly have a talent; for losing credibility.
With the exception of the 5Dmkiii AF system, which you acknowledge, your premise for considering the camera to be a '5Dmkiin' is clearly based upon the fact that it has a dslr form and a sensor of about 20mp.
Canon answered all those users who wanted a fully 'professional grade' 5D mkii and didn't want the cost and bulk of a 1Ds mkiii. Quite apart from the AF, speed, dual cards, shutter durability, stainless steel bottom plate, transmissive lcd display, improved build and weather sealing, the sensor in the mkiii is a substantial improvement over the mkii at high high ISOs, but also has subtle improvements in total graduation and graduation to high and low lights, which give it ( and the other latest generation FF cameras) much more of a film like quality.
Looking at the sales success and feed back from users of the mkiii Canon has clearly produced the finest general purpose dslr of the current era.
However as it looks
like a mkii, and the sensor is more or less the same mp, I suppose there will be those, like yourself, who think it's a mkiin, but then there are those who think the moon's made of cheese.
You've also contradicted yourself with the 6D. In one sentence you call it a '5D mkii v1.1', and in the next paragraph a FF rebel.
The 6D actually does not feel like a 5D at all; it has its own characteristics. It's a fine camera for the market that it is aimed at.