Static Wordpress. Seriously. WP has the biggest selection of themes, and being static practically removes all common security-related hurdles. Other static generators would come second first. Then Ghost, which aims to be the blogging platform that WP used to be.
I second Ghost for that use case, I'm using it for years already for my personal blog (not very active: https://blog.notmyhostna.me) and it's getting better all the time without getting bloated so far. I never really got started with static site generators as it's just too much overhead for me.
If you don't want to self host it and be even closer to the hands off approach of Medium you can just buy the hosted version.
Blogger is still around. So is Wordpress. So is Github pages. Blog hosting is a dime a dozen. If you want a Medium-like layout, you can probably get 95% of it with a couple dozen lines of CSS.
There's a plethora of options.