I'd like to see the marketing study that supports this conclusion. 🙄
Several informal "experiments", I have noted before that a very deep and large gouge in a Tamron Zoom, extending from the center out, could not be made to produce any noticeable effect in one test roll of film purpose shot and processed. I should have asked for the element back when the lens was serviced, it was the worst I have ever seen. I have a feeling it is in Tamron's museum of idiot things happening to their products.
Some of the best glass has bubbles in it.
I did have a lens from my Air Conditioned room fog up, and fog inside definitely was noticeable both visually and in the prints. Fortunately, it cleared up when the lens warmed up. Was in Florida, only woman with me was unwilling to go "David Hamilton" on me.
I used to apply cellophane tape, or finger nail polish to a UV filter to create "dreamy" effects in wedding portraits, and also there are commercial filters for the same thing, which never worked as well as the homemade ones. I had to open up the diaphragm one stop more than the size of the opening to obtain any effect visible in the print, and I had to increase the exposure to compensate for lost light. I experimented to get the most useful filter leaving an oval clear spot in the center and a mark on the ring to aid in mounting the filter on a TLR, plus the best stop to use marked on the case.
I have accidentally left cross star filters attached shooting some flash shots at normal distances, with a definite loss in contrast and some sharpness, but not enough to have to toss the images or do a lot of explaining. Client was not a photographer. ;-)
I had a cheap pre set M42 mount, (I seem to recall it as a Yashica) 60's era zoom, and a shot of a person in bright sun looked as if the person was aglow, -- I foolishly gave this lens away before I considered "signature". It certainly had that old time glow in the images. ;-)
But, the glass had no scratches and there was no dust inside of it, and probably no coatings?
These, perhaps, emulate real life damages to lenses, and that said, I know the first thing people buying lenses for a living do is to shine a flashlight through the lens and check the elements with a lens. They pay close attention to the rear elements.
They also know which lenses can be easily disassembled and reassembled at a reasonable cost to clean up minor dust, haze, and fungus. I hear many good lenses have the elements well mounted so that it is less necessary to have expensive equipment to realign the elements. I have also heard some lenses commonly have lots of interesting things found inside, like metal filings, dust, fungus, oil haze, hair.
Any visible damage or dust probably knocks off half the value of a lens, which may be terrible for the seller and acceptable for the buyer.
And, finally, a beautiful hard multicoating just looks great.
I recently shot a roll with my Avatar Leica I, and it does flare, glow, etc. a bit in bright sun, no visible scratches, but no coating, and I did not have a shade to fit with me. It was sharp and the shutter worked.
We are fortunate to have available to us many lenses that will quite normally shoot far better than we do. ;-)
Perhaps an "Ugly" lens contest should be held, photos taken of and with. I have a 90mm Elmarit with a separation, brassed lens ring, missing leather, missing red dot, well, you get the idea?
Regards, John