Is the Tamron SP 70-200mm F/2.8 Di VC USD Canon really a better choice for 6D Canon than the Canon lens ???
Unbelievable. How could you explain this ?
First, I own neither lens, so I should be careful when stating opinions on them.
On the other hand, I have looked at the charts on The Digital Picture website, and from that I'd have to say that the Canon is still significantly better than the Tamron. When shooting wide open at 200mm, the Tamron gets noticeably softer all over, but particularly in the corners. At 70mm, sure, they are similar, but from the charts at least, the Canon is significantly better on the long end and off the center.
Interestingly, the charts here do not show the same thing, which surprises me. On TDP, the softness of the Tamron is quite pronounced at 200mm compared to the Canon. Quality Control perhaps?