Under high-pixel-density sensors, vintage lenses exhibit issues such as chromatic aberration, flare, and others. Some Leica lenses—even on film—prove especially prone to flare, such as rigid, 35 IV summicron. Just my personal experience
I would write that a little differently, although the gist is the same:
"When imaging onto high-pixel-density sensors, lenses exhibit issues such as chromatic aberration, flare, coma, and others. Some older lenses exhibit imaging with both more kinds of aberrations and greater magnitude to the aberrations, but the age of a lens is not a perfect predictor of such issues. Individual variations, lens by lens, exist in all cases."
Not every lens of a given model will show the same issues, and that there are NO perfect lenses that exhibit no issues at all. With older lenses, where degradation from use, age, and variances from the assembly process of years past will matter more, you'll probably see more issues. But even new lenses exhibit variations.
Most users never see such things clearly because they only ever have one of a given lens at a time. I was in the position many years ago of evaluating lenses to use for ground truth on a project at NASA. We were working with Nikon ... We needed a half dozen 105mm f/2.5 lenses for a particular project. Nikon sent us two dozen, and I was part of the team that tested them on the optical bench and graded them. Of the 24 examples we received, I was able to grade them into four batches from best to poorest ... in the best performing batch, there were nine lenses, so I allocated six lenses for the project, and paid for one of them for myself. The others (none of which were "bad", just not as good as the "best") we sent back to Nikon and they were returned to Nikon's inventory for sale.
I have not found much wrong with my Leica lenses, although they are clearly not the latest, greatest, highest spec lens models available. In the end, regardless of specifications and individual performance, what matters is whether a particular lens suffices for its intended purpose, not whether it is wholly without flaws or is the best or worst example. Many wonderful photographs have been made with lenses which rival a Coke bottle bottom in optical quality...
😉
G