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I'm not sure how the 50L would compare with other 50/1.2 AF lenses available in Canon mount, but compared with the EF 50/1.4, it is considerably more resistant to flare. Here is a very old (by internet standards) test, in well controlled circumstances. About halfway down the page you'll see a comparison of flare handling.
In my use of the 50/1.2L, I've found it to do quite well in backlit situations. There is some fringing of window frames, tree branches ,and so forth, similar to what you get with the 85L, and which can be mitigated in raw conversion. Stopping down can almost eliminate it, but of course shooting at or near wide open is an important reason for owning the lens. Veiling flare is low, and when more clarity is desirable, the clarity controls in Lightroom can help.
I don't see a problem with your lens based on the one sample image. It looks more like a scene/lighting/exposure issue, but of course I wasn't there.