Curious why you think that. Content is still at the URL, a RSS feed is just one way to consume that content. Not sure how using a hosted microservice to generate that method diminishes the premise of owning one’s content.
As long as the content stays at the domain, the url of a micro service can be switched and nothing breaks. IndieWeb at its core just means own your content at your own domain, not DIY everything.
The microservice is indeed not the issue… The issue, as I see it, at least, is that third-party URLs are inherently more brittle (less future-proof) and that a URL using the word “demo” is even less likely to belong to a production or stable server. 🤓