Right out of the gate, this post’s title and its implied question is misleading.
We shouldn’t think in terms of “WordPress.com vs WordPress.org”.
Instead, the correct comparison is WordPress.com vs a Self-Hosted WordPress site.
Why? Primarily, because WordPress.com IS a managed host. WordPress.org is NOT a host.
You can’t go to WordPress.org and “set up a website” that will be available on the Internet.
So, what’s the difference between WordPress.com and WordPress.org? WordPress.com is a service that helps you build a website using the WordPress software with managed hosting, while WordPress.org is the source where you can download the software itself, which you can use to build and maintain a website on your own.