I have a 5D4 and a 7DII.
I have come to really dislike the look of the 7dII images in low light when photographing people. I actually love the 7DII as an all round camera but I don't think its for me with weddings. I load up the images from both cameras in LR and when I come across the 7DII images at higher ISOs, I just do not like them. Also the Auto white balance sucks for low light work... I don't know why.
So I am thinking the 6D might be a good second camera. It would be a backup camera and will have a 35 1.4 or the 24-70II (when the 70-200 is on my 5D4.
Anyway.... I am aware of the "primitive" AF system on the 6D but I am ok with that. I shot sport on a 5D2 so I will be fine. My real question is... will the 6D get me in pretty much the same ballpark as the 5D4 in terms of overall IQ?