Do the network effects and other parts of Medium actually increase readership just by virtue of posting there vs a personal self hosted blog?
I would not trust Medium, especially long-term, and it already has quite a bad reputation in some circles (i.e. I personally tend to avoid Medium links if they don't come well-recommended). If they change in a direction you don't like, you've tied your writing to them - your own domain is a lot more flexible and safe in that regard. On the other hand, people do report larger reach on Medium if they aren't already established. Crossposting gives you access to that, while also maintaining your own place on the web.
But it's a bit tedious at times. Having an "admin panel" accessible from everywhere is very comfortable. But I don't like the bloat monsters like Wordpress, etc.
As for the reach - I think Medium doesn't provide so much value. Posting on HN, Reddit, etc feels enough in my case.
Platforms like Substack & Medium offer you "reach" because they can distribute content at scale. That means less intentionality from your readers, but a higher likelihood some random person finds your work. Reach is great when you're trying to scale your work and get it in front of lots of people. There is no doubt that by virtue of SEO, higher traffic, more organization etc. that platforms like Medium will get your stuff in front of more people.
Personal blogs offer a level of complete ownership and customization. I cannot tell you how often Medium, Mailchimp, Substack etc have disappointed me in how I can monitor the traffic to my publication, or even have a custom URL for SEO purposes.
Personally, I optimize for reach > customization starting out. The benefits of more eyeballs on my work far outweighs my need to customize when building from the ground up. But that's primarily due to the fact that my content is designed for more folks to see it.
(Source: I write about video games every week @ www.pausebutton.news)
edit: I'm sure there could be some sort of decentralized approach that can mimic mediums tag functionality via ActivityPub. That would be the best of both worlds, discoverability and independence.
You can always cross post on Medium and other such services. Just got to remember include the canonical URL.
That way you get the advantage of being searched on services like Medium, Dev.to and others (although, I don't think this is much since most search via Google). And you get the advantage of owning the content and your own personal brand.
I recently came across a popular new blogging platform - Hashnode. It has a decent balance between ownership (sync to repo) and distribution (their community).