I think Medium is great.
I pitched an article to an online magazine, about UBI. They said they ran one too recently, so I figured I'd self publish. I could have put it on my site, read by zero people, but I figured a medium.com URL would get farther wherever I submitted it.
I was right, but not only that, the Medium twitter account tweeted my article, and Medium asked if they could edit it and make an audio version.
Many interesting things came of this signal boosting. People started emailing me from weird places, like economics professors and government researchers, including one guy at the World Bank. I was invited into a secret slack that I'm still part of today (unfortunately most of the good internet is going the way of non-public places, but that's another topic). The net result of one article they boosted has been meeting a lot of people who are now my friends, two years on. Kind of amazing in retrospect. Medium's boosting also allowed me to gather enough Twitter followers to feel like its a useful platform, in a sense unlocking "my own" audience.
None of this would have happened if I self hosted. About these issues of canonical URL, why would I care? If I self hosted almost no one would have read it. I am more interested in reading and writing than I am in canonical URLs or a small bar on my screen. I suppose its unfortunate if it annoys 90% of my readers, but that's a lot better than no readers.
So thanks Medium.
(my only nit is that their editors changed some of my language to be more snarky, so I would not let them edit again)