To the folks saying the revenue multiple is crazy: remember that the $9MM revenue is substack's cut, not GMV (gross merchandise value: the amount subscribers paid).
If you're comparing substack with a non-marketplace business, you probably want to compare gross profit between the two, or compare substack's GMV with the other company's revenue.
Most startups that Substack is competing with for funding (mostly SaaS services) get to keep 100% of their GMV. So using $9M as their revenue number is the right way to value them.
Cost of goods sold is always deducted before reporting revenue, otherwise companies like Uber, Lyft, Doordash, Amazon, Stripe, Square that pass through most of their receipts would all seem 10-100x bigger than they actually are.
The potential "capturable" net income from operations is what matters in the end.
Retail tends to have large revenues and tiny margins. I can say Amazon retail should be worth more based on their revenue, but when their margins are 0 or negative, that would be dumb
If you're comparing substack with a non-marketplace business, you probably want to compare gross profit between the two, or compare substack's GMV with the other company's revenue.
Also consider growth expectations.