It doesn't cost anything and there's no ads. Even linking your domain to it used to be free (sadly no longer true). It has a very decent writing experience and the out of the box design is simple but effective. It has a reasonable amount of customization. It has wide support for apps.
It's part of a network so you get functionality like claps, a comment system, followers, the like. Blogging with a "social network" built-in. It has newsletter support.
I think that's a sweet deal for such low (or even zero) costs. Ultimately I'd think your writing is what the value of your blog is, not the behind-the-scenes technical tinkering. Unless that really is your thing.
Should you be paranoid about Medium going under, there's an export option.
Note that I'm the kind of person that wrote my own blogging software in the early 2000s. Tinkered and managed it that way for well over a decade.
I've given up on it. It's time wasted. Nobody cares about your blog design, it's hard enough for anybody to care about the actual text in today's landscape. Hence, pick your battles, keep it simple.