Honestly, Bernard, you do keep bangin' away at that old drum.
There are two fields in which DSLR's are still more prevalent - Fashion and Sports.
For the rest mirrorless clearly has the momentum.
Hum... I still prefer the ISO64 mode of my D850 for landscape as well as the superior color rendering and quite a few other things as well (better weather sealing that works, the ability to display in parallel 2 parts of an image for T/S shooting, better battery life in the field,...), so I have to disagree your assessment is an objective one.
The a7rIII is an excellent landscape camera, but there is no objective fact supporting the proposition that it is the best option today.
Will the a7rIV be superior to the D860? There are many reasons to think it will be, but I am taking pictures with cameras available today, not with a potentiality for future superiority.

This is why I keep saying the same thing... the a7rIII is an amazing and very desirable camera. It offer the best bang for the buck per gram and per cubic inch... but it is being overhyped a bit when described as the best available option
today. Besides, by the time the a7RIV is out, we will have options from Canon and Nikon on the table as well and it will not be any longer about mirrorless vs DSLR but about comparing various mirrorless options.
And overall, I am not even speaking about the ability to get access to some unique lenses with fully working AF functionality. I could simply not have taken this image with an a7rIII. Close yes, but not exactly the same rendering. Now we can of course discuss whether close is good enough or not, but I see no value in regressing at this point just for the sake of being on the trendy momentum train.
D5 + 200mm f2.0 at f2.0 / the 10 years old versionCheers,
Bernard