Who is writing here and also maintain a professional blog?

Having your personal blog is good from employee branding perspective. Especially if you combine it with some portfolio page. It allows you to create a kind of "go to" place for your colleagues and recruiters.

Dev.to of course give you a better audience. It would be great if Dev.to allowed to create such a personal, customizable blog-page, something like dev.to/sosnowski and maybe event connect a custom domain to it.

You can combine the two, have a personal blog but republish on dev.to/medium for the audience and conversation. (Both dev.to and medium supports canonical urls)
(As an example see loftie.com/post/programming-music/, at the bottom link back to dev.to for comments)

Having your personal blog is great to maintain control over your own content/brand, and prevents situations like with medium where they change the user experience for the negative. Dev.to seems less likely to do that though, being opensource and generally more developer friendly.

I've just started writing my own blog on WordPress this month. I've been toying with the idea for literally over a decade, but I always found excuses why not to write - thoughts like "Everything have already been written", or "I know myself, I'll just write a few posts and then forget about it", and of course the "What if I'm not good enough?" (That's the worst. You're a professional. You are actually getting paid to write code. Do you think your boss is that dumb to pay you if you're no good? or all the previous ones, for that matter?)

Well, I finally realized I don't have to be Jon Skeet or Eric Lippert to write about c#, and I don't have to be Aaron Bertrand or Jeff Moden to write about TSQL.
The internet is big and there's a place for everyone. As long as you write about stuff you know, you're good.