I am not sure they made a "worse" version. From what I've seen, the 6DII is an improvement over the first version in almost every way.

The disappointment seems to mostly be focus around the sensor. It seems that while canon has put new sensor tech (on chip Analog-digital converter) in all new cameras, including entry level crop sensor cameras, it seems they chose to use and older tech sensor in the 6DII.

This should mostly "affect" lower ISO shots and anything above ~ISO 800 should be comparable.

As I still shoot the 5DIII that has older tech, I am not getting to caught up in it. My guess is that Canon used older tech to save money on the 6DII sensor to help keep the price point down (and their profits up).

Not having handled one, my guess is it is an exceptional camera that will take millions of great images. That the sensor is likely better than the one in my 5DIII. But there will be a few reviews always fixated on its weaknesses.