>>3691819>>3691732Pic related is just some examples of high res cameras outperforming the A7SII in ISO performance.
A7RII has 42.5mp, DC-S1R has 47.3mp.
Both are about 3.5 to almost 4x the resolution, yet perform slightly better.
Also note in the graph, how every single one of these cameras performs very poorly above 25.6k, making it being able to reach higher ISOs a moot point.
Lower mp count does have its place though. It eats up far less memory, can make a workflow significantly faster (especially important for sports and journalists) and it is easier to make good low light performance because the microlens performance is not nearly as important.