To JERRERYG:
You can very very quickly demonstrate the 'focal shift'.
1 Take your camera, place on a tripod. Tilt it down carefully!!!
2 Put a newspaper on the kitchen table with good lighting.
3 Use live view and zoom in. Focus at f1.2 on a line of text in the middle of a paragraph. AV Mode
4 Turn off live mode now and take a photo.
***Touch NOTHING but the AV wheel***
Do NOT refocus or turn on live view.
5 Stop it to f1.4 and take a shot, then f2.0 and take a shot.
6 Compare the three on a computer.
The second and third shot's focus will have 'jumped' to another line.
That is the dreaded 'focal shift' the armchair QB's are crying over.
It is the same Aspherical element that create the dreamy bokeh, that causes the shift optically.
https://en.wikipedia.org/wiki/Aspheric_lens
With the 85L II, and the same test, the printed text won't 'shift' ONLY the DOF will increase.
If you are a Pro Photographer, shooting at f2.0 using AF on a model's eye for example
This shift will cause OOF shots whereas a 85L II will not.
Lastly I will say, using this lens myself testing outside in real world conditions, I found my own tiny movements
while using this lens at any wide aperture to be USER error 99% of the time, and 'focal shift' maybe 1%
One thing that is often overlooked as a case of OOF shots handheld. For the most part, the lens's Focal Plane is flat.
Tilting the camera up or down, left or right cause just as much errors as a thin DOF.
The combination of the time creates a real challenge wide open handheld.
Nailing a great shot at f1.2 handheld is it's own reward, but I am a hobbyist.
I don't answer to potential upset clients, only myself.