That's what happens when we abandon protocols (RSS feeds) in favor of walled gardens.
Yes, in general terms, there's always an abstract discussion about RSS vs Facebook,Twitter,Google AMP, etc.
However, your particular comment is not relevant to this particular blog post. The RSS protocol is "free" but that doesn't matter if it does not address the targets that Facebook does.
(Besides that, the journalist writes for DennikN and they didn't "abandon" the RSS feed. It's at: https://dennikn.sk/rss-odber/)
We can't just reflexively reply with "RSS" every time the trigger word "Facebook" comes up. It needs to be relevant. RSS is not applicable to what the journalist is talking about. RSS is not relevant to the perspective of the publisher for metrics of "audience reach". RSS feed is a convenience tool for the reader and the blog post isn't about that perspective.