Author here. One thing I think Substack helps a lot, and that I didn't mention in the article, is on its network effects.

I started this blog last year, got it featured on HN home page a few times, but my own newsletter[1] (not hosted at Substack :) growth is non-existent — so far, it got only 25 subscribers.

Meanwhile, people can cross-recommend newsletters on Substack, and leverage things like Notes (and replies to popular writers) to increase their subscription list. That's another aspecto of this whole Substack eating the (newsletter) world that I fear: that at some point, people could get so used to subscribe only to Substack newsletters that any form on the open web will look weird and/or suspicious.

[1] If you're feeling it, you can subscribe for free here from there (blue letter icon on top menu); I only send occasional messages: https://notes.ghed.in/