Success! I just partially implemented Webmentions for my website. Although I haven't figured out a good way to receive Webmentions yet, I'm able to send them. Fortunately most of the work was done, as detailed in the post Sending Webmentions with F#. The rest was mainly a matter of adapting it to my static site generator.
What does this mean? It means I can comment on any website I want, regardless of whether they allow comments or not. As if that weren't enough, I have full ownership of my content as my website is the single source of truth. As a bonus, if the website I comment on supports receiving Webmentions, my post will be displayed on their website / articles as a comment. The next step is to handle deleted comments, but so far I'm happy with the progress.