Wordpress provides more bells and whistles for better SEO compared to medium. Medium is good for distribution. We host our own wordpress and got to top 1-3 google results for relevant keywords in a couple of months.
Backlinks is one of the most important pillars of SEO, but the backlink needs to be to your domain like example.com/blog, not to Medium’s domain. Medium is definitely good for viral sharing since they have a nice “repost” feature, but I wouldn’t depend on it for your SEO needs. For us, we set up a static Jekyll site and host on Github pages which is dead simple to deploy and can write in markdown in any editor. There is no database to worry about when scaling, no clumsy editor, etc 😉 If you want more of the admin interface/text editor/guest post submission then look at Wordpress or Ghost depending on if you like PHP or Node. Any content strategy always requires multiple things. 1. Content on your own site for SEO, content on other sites for backlink building and distribution, etc.