Apparently the low light performance of the full-frame Sonys is a combination of IBIS (mechanical in-body image stabilization) and Back-Side Illuminated (BSI) sensors. The Sony A6600 (APC) has IBIS, the A6700 adds BSI. Other camera manufacturers also offer BSI sensors.
Oh, my D850 has one of those. It does perform very well in low light, but those extra stops of dynamic range in my view count most when they're yielding more contrast in an adequately lit scene - admittedly a privilege, and one I can more often afford myself with the kind of shots I like to take. I do print my work, though, and there's nothing else like that to show the limits of even a very good display.