If the 6D were "so much better" than it really is, and still significantly cheaper than the 5DIII, why would anyone buy the 5DIII? (Or, put differently, why would Canon have released the 6D at all?)
Well, that's something for Canon to figure out, as they are in the business of selling cameras, not me.
But the 6D should have been better.
I feel that in their efforts to differentiate it from the 5DIII, Canon ended up compromising the 6D.
That's not smart.
Instead, Canon should have put extra efforts in proper differentiation without compromising the 6D.