Your website (blog) is your home on the internet. Would you give someone else - a stranger - the keys to your home?
This might seem weird posted on 200wordsaday, but I don't consider the two to be comparable. I'm using 200wordsaday to just write and getting into the habit. When there will be canonical links I'm planning to crosspost the best articles to my personal blog.
Medium on the other hand is used to publish and get readers. Without Medium you lose your readers, that's why its lock in mechanism is so strong.
Your blog is your home
For someone who just wants to write Medium might seem great, you just write and that's it. They take care of getting you in front of eyeballs.
When you start on Medium is really hard to move. Even freecodecamp with millions of views and followers is having a really hard time trying to move off the platform.
If you're a smaller writer and if your blog is personal having your own brand to it matter.
Your own place to write. Your own brand. Your own space. Your home.
Giving control to someone else, no matter who,has its drawbacks. If you're aware of them and you go in knowingly all is good, the problems arise when you don't realize there are drawbacks or you downplay them.
That's why I don't like writing long form pieces on Twitter/Facebook or social media.
People are there in drowes and it's easy to get noticed, but at what cost?
Don't get me wrong, as a reader i love Medium. I love the design and i love the convenience. As a writer I wonder what we're losing by giving up control like that. And if it's worth what we get in return.
Publications give you more readers and let you expand your reach, but they could do that by just having a website and letting people guest post directly. That way they would get back the control they now give to Medium.
Have your own blog. Crosspost on medium publications that allow you to do it for exposure (if you care at all about that sort of thing).
Don't be too scared. It's easy to open a blog. You don't need to know anything about websites.