I definitely see the author's points, but I disagree with the proposed solution. Feed discoverability should be a basic browser feature, not something web developers need to actively implement, nor some information that users have to scrape themselves from the DOM.
I made an extension back in the day that parses the tags and puts back the feed icon where it's supposed to be (on the right side of the URL bar), and also renders the feeds properly rather than just spitting out the raw XML : https://addons.mozilla.org/en-US/firefox/addon/rss-viewer/
This is how the web used to work 10 years ago. The tag has a purpose: it instructs browsers that the current page has a feed, so the browser can parse it and show a feed button to the user. Both Firefox and Chrome used to work this way 10 years ago.
Then motherfucking evil Google began its war against feeds. First it killed Google Reader, then it stopped complying with the conventions, removed the feed icon from their browser and stopped rendering RSS/Atom. Firefox quickly complied too.
Let's make it clear once and for all: yes, I, can add an RSS URL to my website to make discoverability easier, but it's not my job as a web developer to explicitly make feed discoverability easier by modifying my frontend. That's just a workaround. My job as a web developer should be to provide the right element, and then the browser should know what to do with it. Just like the browser is supposed to know what to do with scrollbars if my divs exceed the window size.
And, as a user, I shouldn't write my custom JavaScript to parse the feed URL from the DOM. Just like I'm not expected to write my JS user script to render the title of the page. If browsers refuse to provide such basic features, then it's a browser problem. I would say "choose a browser that natively supports feeds", but there's none left. So use extensions to mitigate the impact of feed-hostile browser politics.