Nikon Df real-world samples gallery
Try going by raws from the D4/Df and A7. The link is to A7R samples, which is a different camera that will be worse at high ISOs than the A7, and the OP referred to the A7, not A7R.
So yeah, a lot of people going for the Df will seek it out for low light+high ISOs. Anyhow the D610 is likely a good bit better in lowlight than the A7, irony that’s a very similar Sony sensor to the A7's.
I think the A7 is an interesting first start for Sony’s FF mirrorless systems, but there are problems that Nikon has worked out for its DSLRs.
This statement above: “and I am sure very high percentage of the photographers shoot during day time” is preposterous. Like saying cars aren’t driven in the rain.
More likely at least 2 stops in the shadows.