Data point: I've never browsed Substack for content. I have no idea what may or may not be on the platform, and I don't really care. The quality of the median post - or author - could decline any amount, and I wouldn't even realise.

I've subscribed to multiple Substack newsletters because content creators I already liked moved or launched new projects on Substack.

Obviously everyone is different, but my impression is that Medium was trying to sell the "Medium brand", and struggled because a lot of people didn't find the "Medium brand" worth $5/month. Conversely, Substack is a platform for people to sell their own brands, and a lot of people find those brands to be worth $5 (or $8, or even $10 in some cases) per month.

Will people now subscribed to slowboring.com suddenly stop in significant numbers because there's another blog/newsletter built on the same platform somewhere which is really low quality? How would they learn this, and having done so, why would they care? In another comment, you say:

> [LCD blogspam] will devalue anything published solely on Substack

I don't value anything now because it's published on Substack. How can you devalue zero? :)