Yeah, it's interesting that the 6D is a lower end camera then the 5D and 5D2, but yet most people preferred the 6D especially in terms of High ISO night time photography. And many people still use the 6D today.I originally bought a 6D as a backup for my 5D MkII and ended using the 6D full time once I looked at the images. Especially for low light. I still have my 6D.
Canon I would say led the charge out of the gate for DSLR's. Nikon had catching up to do. When Nikon caught up with the D700, to me it felt like Canon was sitting back a bit lazy. They finally got off their butts with the 5D3. And from that period on, I think Canon, Nikon and Sony have all made great strides.
With Mirrorless it was Sony that took the lead, Canon then got in the race with some really good offerings and this time it was Nikon who was late to the game. I would say none of Nikon's mirrorless offerings were very impressive at all. Their Z7's and Z6's were simply just mirrorless equivalents to their DLSR cameras. It wasn't until the Z9 and Z8 cameras were released that Nikon finally made mirrorless cameras that could be considered an upgrade to the DSLR's. That's why it's only now, that I finally got the Z8.
Anyway, that's my superficial view on digital camera history from 40,000 feet.