Apple are really such filth. Imagine thinking it's ok to take 30% of every transaction like this, and like they already do on their app store. I don't know how anyone thinks this is ok. It's worse than credit card rates.
Patreon wants to advertise and publish content in an iOS app. Apple says you must allow in-app-purchases. Either there is value in being on the platform or there isn't. Patreon seems to think there is.
To creators there is no cost, by default the price of their subscription offerings will be bumped up so they get the same revenue. Patreon will also increase revenue by taking the same % of the higher overall price.
Users will have the choice of subscribing through iOS or through the website. If the higher cost from within the app isn't worth it to them, they will go to the website.
Who cares?