Then I "switched" to Substack 3 years ago and the audience growth is real. I'm approaching 2000 subscribers (some of which are paid, which always surprises me and I appreciate), and these keep growing organically although I'm sure a large portion of which are fake. It's hard to say it doesn't work or isn't worth it.
Now... spoiler: I never "switched" to Substack. I continue to write all of my content on my website _first_, with all of the features it had before, but now I copy/paste the content into Substack and distribute it that way. It's painful, but I have scars from when I moved off of Medium and want to ensure I "own" the originals.
If you are curious, I had written more about this 2 years ago in https://blogsystem5.substack.com/p/20-years-of-blogging