I have old books, where Mary Ellen Mark, among others, talked about how remarkable, the old Leica 28 mm lens was.
Wasn't there an issue of Leica having to redesign their wide-angle lenses, to clear the meter flag. I believe, they went to a retro-focus wide angle design, duplicating their SLR lenses.
I have experience using this design with a Minolta CLE, I used to own. I used the 28 mm Summicron, ( the one that took the 48 mm filters ).
I now use a Contax G2, with the 28 mm Biogon. This is a true wide angle design. I understand what Mary Ellen Mark, was talking about. This lens, stretches like a 24 mm, but without the distortion. I always thought that 28 mm was boring, until I shot with that lens.
If this was done because of the M5 & CL, ( meter flag ), then I say, that Leica should have been vilified, because, when they went to the M4-2, they didn't bring back the better, ( in my opinion
& apparently others ), design.