I did a comparison of those 2 lenses with the Canon 50/1.4. I found that the Canon is faster (i.e. brighter in terms of T-stop or light transmittance) than the Zuiko f/1.2 lenses. But there wasn't a lot in it.So there are people with taste for older glass on this forum too. I'd turf out your fungus lens before it infects others and recommend you try the Rokkor 58/1.2.... you will like it.
To business - I'm deeply skeptical that the T-stop of the OM 50/1.2 is slower than the EF 50/1.4. Although there should only be 1/3 stop in it, none of your cameras are capable of detecting light that comes from faster than f/1.6. The 7D (iirc used for your test) is not capable of detecting light from a cone faster than f/2.
Nevertheless, Canon cameras appear to register better sensitivity when coupled to EF lenses. This is because the camera knows that it's connected to a fast lens and silently boosts its ISO. Of course, it has no idea about the OM 50/1.2, so it does nothing and gives you a faithful measure of the detected light.
I tested this quite carefully - the trick is to partially rotate the lens so that the electrical connection is severed - it's real. Curiously, my ZE 35/1.4 and Sigma 50/1.4 lenses also appear to be faster than they really are...
Others tested the 50L and found it behaves like a 50/1.6 on a 1D4 / 5D2 and a 50/2 on a 7D. I can't speak to a 5D3 - I decided that I'd be upgrading when I got to be better than my camera.
Canon is not the only culprit caught up in this game. Nikon, Sony and Pentax were also caught cheating customers out of large aperture. Per my comments, my Fuji X-E1 doesn't cheat with SLR lenses (but I've no idea whether it does with fast Fuji lenses.)
Now all this returns to the question of which lens is sharpest wide open. Well, the short answer is they're all pretty good at f/1.6 and excellent at f/2. Since the sensor doesn't actually detect light from a fast cone, it can't contribute to the bokeh - but since it's inside the mirror box, it could bounce around and degrade the contrast. Bear in mind that there's more than half a stop between f/1.6 and f/1.2 so 30% of the light intercepted by the lens is bouncing around...
I used the 7D in fully-manual mode with 1/50s and the lenses wide-open.
I have a hard time believing the Canon camera is silently boosting its ISO.
What ISO gets reported in the EXIF data?
The Canon 50/1.4 produced a slightly brighter photograph than the Olympus 50/1.2.
I am not saying you're lying. I am saying I find it hard to believe.