I have two - I like it, but it takes tons of time. One of mine is an extension of a blog I already write on education - a clear niche and a network to reach out to - I get 1.5 new subscribers a day on that one (about 5 new paid subs a month) - the one on consumer issues is taking a lot longer to build, but is starting (after a year+) to build an audience.

The lack of a built-in audience and the value prop for readers mean you have to do a TON of work to actually earn from your Substack - unless, as you note, you're already a celebrity.