Hi,
Since some people replied to my 5th point, I'd say:
I also own many L lenses, and had to return many times to get a multi-thousand dollars Lens working "as expected".
With that I mean: 2 copies (of different models) were AWFUL. Unacceptable blurred left or right area of the frame, no matter the aperture. In fact the appetite doesn't help much (if anything) when optical elements are misaligned...
If a company sells $2 - $3K (or even 10K) Lenses, any normal customer would expect it's working fine. I know some copies may do better, but not that way...
Just remember one IMPORTANT THING:
In USA you can Return a lens until you're satisfied with the copy you get. But is NOT always possible in other countries...
Several times, when explaining the problem, other people told me "but you can return it until the good copy". Well, unfortunately not. That's only in US, CA, Europe and some few other countries/regions.
So, for me, be Sony (with even more expensive optics), Canon or Nikon, they
should increase the QC of lenses, which lot of times are 2, 3 or more times the cost of the camera itself in the Pro field.
In fact they do it. But it seems too low for so expensive Pro product.
Testing individually is done at certain level. But need to implement an industrial procedure, not by humans, to ensure better QC.
It's not so difficult at all. These companies are leaders in optics and can perfectly check the proper alignment in a automated array of production. "Engineering" speaking is not that difficult, nor so much more expensive.
The more expensive cost comes when they detect so many variants or worse, "bad copies", that require to go back if they want to KEEP A PRO STANDARD (as supposed..), at least for the "Best in class" line of lenses they sell.
It should be done for such expensive lenses. As well as they test the cameras.
Don't get me wrong, Nothing is "100% error free".
But sometimes they're out of the obvious & expected "normal" quality standards.
PS: I do know LensRentals. They know this problem very well, as Bryan at the-digital-picture does.
PPS: Sorry for my typos, from smartphone is not that easy