Some things I don't get.
For 7 years I've been using Contax/Zeiss lenses on my contax 645 with an aptus 22, Leaf Valeo, Phase -30+, and P21+.
Now I use them with the Leica Convertor on the S2.
I've rarely see any need for correction in post, except for the rare CA when shooting wide open in bright back light.
The Zeiss are always brutally sharp, actually a little too sharp though sharper than the Leica 120 I own, though the leica (to me) has a prettier character.
Now the flip side of this is my 43 lenses and cameras. I have a bag full of Olympus m43 primes I use on the em-1, em-5 and gh3's.
On the Olympus and panasonic they are sharp, crazy sharp, but they seem to lack some character and I'm sure there are a lot of behind the scenes correction going on in the camera, or the lens/camera or the lens/camera/software.
The reason I think this is when I mount Leica M mount lenses on the m43 cameras, the leica lenses display softness, severe ca but used on an m8 they are fine.
Also Interesting is the Pansonic lenses aren't quite as sharp, especially the zooms but have much nicer roll off and character to them the the Zeiss/Pansonic lenses continue with this look, though don't have that extreme bite of sharpness of the Contax lenses.
Not that it matters, other than in the final look, but using the contax lenses, some older film lenses like Nikors I'm amazed that they need very little post correction and hold up extremely well, considering they are 10, 12 who knows how old designs.
I personally think the less digital correction needed the better the lens, though in all honesty, the prettiest lens I've ever used, film or digital is the old boris Hartblei tilt shift in a contax mount.
It's not really crazy sharp, surely not pixel peeping sharp, but has the most beautiful roll off of any lenses I've used.
P.S. I doubt seriously if Leica would out and out lie about using digital corrections if they didn't. Maybe I'm naive, but to me that would open up a very not nice door that would be hard to shut and Leica has too much brand equity to lose.