Couldn't agree more, the beauty of a picture cannot be meassured in a lab. That beinh said, apparebtly lab tests show that some old f-mount lenses don't use the full resolution of 36 MP plus sensors. Whether or not that is actually bad, or if you would notice the difference with the naked eye, is something different.

Thay being said, I'd never replace a lense unless it either broken or I see negative impacts on image quality. If none of that applies I don't see a reason to spend a fortune on new glass just because. Unless of course I want that lens.