the problem here is that it is so hard to find side by side images from another lens shot from the same spot at the same f stop. In the shot posted above the background is full of vertical lines so it is not too surprising that the image is, well, liney. I suspect many lenses would have done similarly and a fair few a lot worse. In my experience, the ZMs are comparatively gentle in the OOF areas and that includes the planar. The vast majority of images I have seen from both (incl my own) have very subtle OOF indeed and the same cannot be said for some other lenses. In fact, the lenses have such a creamy rendition that I was amazed to find some portraits shot in parkland (with trees, twigs etc behind the subject) left the background positively melting away. That said, a lens with lower corrections, lower resolution and contrast will tend to produce softer bokeh. some of my cheap canon AF zooms have lovely bokeh wide open at f4 (and soft subjects) 😉 Also, on the example posted, try tilting your head so the railings are not diagonal but vertical and you will see a very large proportion of the craziness vanishes. Guess the brain makes diagonal fuzzy lines seem a lot worse. The road lines are a bit odd though, granted.
The thing to remember here is that someone can own a lens, shoot unforgiving subjects, decide that they hate it and sell it without ever realising that the Bokeh God would have done just as badly! The test done by Guy Manusco and the Summarit 35, summicron V4 etc is a case in point. The V4 looks horrid compared to the summarit when the subject has pointy plants behind her. The summarit turns them to cream. does not mean the V4 has crappy bokeh though...