Dear @evan, @FediverseSymbol,
what other follows are there? However it doesn't have to stop there. A mutual follow is 2 one-way follows. Feedback is what comes after or on-top follow. At first there is the notification which I never have seen other than being one-way.
However feed subscriptions were anonymous and therefore e.g. not easily blockable.
Btw. https://www.w3.org/TR/websub/ allowed for expiring subscriptions. That would solve the mastodon account deletion avalanche issue. Imagine 3-monthly (automatically) renewing follows. We should do the math what that means for the amount of maintenance messages. The burden of maintaining a subscription would be on the subscriber side rather than the publisher which IMO would be a good thing.