Okey, let me express myself a bit more clear. Canon is definitely able to make high-res sensors, it also able to make amazing prototypes in lab.
The file quality improvement in lower ISO from 5Dmk2 to 5Dmk3 is negligible, and I really can not find a reason for it. For this reason I have been thinking about jump ship to Nikon or go MF for a while. A camera packed with 2012 funtion and 2007 IQ(1dsmk3) is really disappointing.
I am now almost always use Capture One to convert CR2s just to get the file a bit more retouching friendly.
From what I've read in seemingly dozens of similar debates on here, Canon focused on other things when designing the 5D3 - autofocus and high ISO in particular - because that's what people wanted. I wasn't following things back then, but apparently that's what people were clamouring for - the DR/ultra high resolution/low ISO quality stuff has only come along since then.
The low ISO quality issues have always been there.
The DR disadvantage only since the Exmor sensor started appearing.
Canon only really fixed one thing with the 5D3: AF.