For 35mm this is the most efficient approach and Leitz did spectacular job.
I'm going to stick my neck out and comment without reference to tests. I have used a Leitz 40/2.8, 50/4.5 and El Nikkor 50/2.8. The 40/2.8 was the sharpest under the loupe. A clean late Leitz 50/4.5 and El Nikkor are similar. I have Leitz 50/4.5s which have lower contrast than the El Nikkor. Condition of the lens make a large difference. The older Leitz optics tend to not be as clean as a late model El Nikkor.
Thanks for your interesting post. My only experience with Leitz lenses is with a 50mm f4.5 Focatar 2, although my findings are broadly in line with yours here. Prior to getting the Focatar, my go-to lens for 35mm was a Minolta CE Rokkar 50mm f2.8. In comparison, the Focatar is slightly less contrasty, but does resolve just a tad more detail, and I significantly prefer the tonality to the much more "in your face" Minolta. I've used both lenses in Condenser (Focamat 1b) and Diffusion (Durst) enlargers, and have a similar preference for the Focatar in both.