This is what I would call shameless biasing, not supported by hard evidence.
This is a link you posted in another thread with tests of these lenses.
You might want to review them(...)
But, your precious Canon 55mm /1.2 isn't fault free.
You claimed the Zuiko has more coma, flare and less contrast than the Canon.
In fact the 2 are very similar.
The tests only show part of the story; I say this based on my actual experience using them and i'm positive regarding the difference in contrast.
You can read the tests in many ways. If you want me to pick on a difference that could explain my feelings, it was perhaps the flare levels reported by the test. The Canon has the
minimum flare (0.6%) of all the f1.2 lenses on the text, and the Olympus has the
maximum one (1.4%). This robs contrast (i often shoot backlit subjects. Perhaps i almost exclusively shoot backlit stuff!)
Again, if we want to read the tests (i prefer actual use, though), i could explain the lesser contrast by looking at the spherical aberration of each lens. A lens with spherical aberration shows the following on the spot diagram:
Each point gets a 'halo' that robs contrast. The definition is there, but the contrast goes down.
More spot diagrams
We don't know more details on the test, but the Oly shows 0.03mm for spherical aberration while the Canon shows "None". Also the Canon is remarkably free of astigmatism on the center and edge. This is good for clarity and for uniform blur or (bokeh), which this lens shows.
This gives you a hint on the "clarity" of the lens, because for the MTF ("contrast versus ines per mm") test they shoot a test chart against a wall, which is a flat subject, and any curvature of field will make a lens look poor on this test; a lens that would otherwise perform pretty good shooting real life subjects, which as you know, are not flat as a wall. The Canon and the Zuiko show rather similar results on the MTF tests, but I contend there is a difference.
Anyways, all these are meaningless numbers, again, the actual image are what counts; actual performance with 3D subjects, foreground, background, longer distances than when shooting a test chart. And you will find the the Zuiko lovers don't rate the Zuiko 55/1.2 highly, while the Canon FD 55/1.2 (and FL 55/1.2, which has identical design, introduced 1968!) is very well liked.
And that was my conclusion as well.