The Real Cost of Mirrorless Cameras: Art vs Science? Nikon Z8 vs Df

The Nikon Z8 is bigger and heavier than a ten year old DSLR in the Nikon Df, so what did we gain by losing the mirror?  If you’re starting out today, for work or play - is it mechanical operation or soulless computation?  Objective performance vs subjective preference. Art Vs Science?