TIL Patreon's estimated revenue in 2021 is $160m, and Substack's is $11.9m.

Anecdotal but I don't know anyone using Patreon yet know tons on Substack. Would have assumed less of a delta.

cma.xyz. Founder /paragraph, previously at Google and Coinbase

Yes, as said in other replies: Patreon is much broader, and around much longer. I wonder what the numbers are for alternatives to Patreon, such as Buy Me A Coffee and Ko-Fi. 
I think what's also very interesting, is that not only the creators on these platforms are more diverse, the way supporters can intereact are too

A teller / of stories, that is me. / Curious to learn new ways to see. / Proud dad of two. Now, what / about you? | Builds https://paragraph.xyz/@trpplffct

First of all there's the tip-jar functionality, giving supporters the one-off option. Then there are things like extra's etcetera. So supporters have much more ways to reward a creator. For one piece, for a commissioned work of art, etcetera. Buy Me A Coffee now also has a whishlist app. The user choice is better.