While I agree with your overall sentiment that lead to your change, one thing your not realizing (or chose to ignore) is that Medium is a third-party that you are housing your content on. If at any time Medium decides that your blog breaks any rules, your account breaks any terms, for whatever reason — your content is gone. They can remove your blog/account and that’s that. If you have pretty tame content it may be nothing to be worried about. But what if it’s not even a content violation, and maybe how you market your blog?
I experienced a not-so-cool time with Tumblr, when they removed all my blog content within a single day, years of blogging went down the drain, all because of what I perceive to be a misunderstanding. You can read about my story here: http://bitshare.cm/news/why-you-should-never-use-tumblr-as-a-professional-blogging-platform/
What I am saying is that it’s a risk, probably a small one, but is it worth it if it happens to you (to lose all your content)? Probably not, so being able to control my own content and whether or not it gets “deleted from the internet” or not, is important enough for me not to move to Medium, or any other third-party platform ever again.