Substack is what happens when the mainstream media elites overplay their hand and force heterodox writers out of the "mainstream". As it turns out there are still plenty of people who want to read this kind of writing, and we don't appreciate the gatekeeping from formerly reputable sources.
The world already has enough clickbait and hot takes. Substack will probably make a lot of money, but it won’t increase the quality of journalism in the US. We need less opinion in our news diet not more.
There still are such news sources -- The Economist, Reuters, AP, etc., rarely editorialize their articles. Most other mainstream news sources like NYT, WSJ, etc., are just as clickbaity and cater to a specific demographic of the society just like Substack writers do. So I don't see it as a loss for journalism if people stopped subscribing to, say The Guardian, and instead supported a Substack writer.