After shooting Canon DSLRs for over 20 years and investing a lot in Canon lenses, I decided to try the a7r III after reading reviews that said it now had one of the best focus systems available and Sony was making very good lenses.

It is the best autofocus system I have ever used, better than the D750.For starters

Love both systems, about sony love this 42mp , weight and focus system

When paired with the right lenses, it is a relatively compact system.

If you resort to video or the LCD, you get very poor AF.Sony has a fantastic AF system that can seamlessly go between the viewfinder and the LCD.

Nikon's great autofocus system only works with the viewfinder.

The D850 has a fantastic autofocus system taken from their flagship sports camera.

Sony had superior dynamic range and an excellent electronic viewfinder, although the a7R ii also had an under-powered battery, mushy control buttons and truly awful menu system.