To be honest, i don’t think politics is a concern here for Cock.li but rather reliability and security. Smaller providers don’t have the resources to manage large amounts of users compared to established companies. I don’t think it is inherently a political service, it just happens to be popular with users who need anonymous throwaway emails.
Riseup on the other hand is meant to be very political but also suffers from the exact same problem of being underfunded. Being invite only also does not help.
Email is decentralized so E2EE has little utility if it only works where people use the same provider. At that point they would be better off using a real messenger.
Cock.li’s primary benefit its easier to sign up through Tor as a complete burner account, without taking potentially doxxy steps to “verify your account”. Proton’s insistence on verifying they’re human by using another email service or number and sometimes blocking Tor users - while understandable to prevent spam - has led to people getting arrested because the second provider they used was tied to their identity.
So in my opinion, its more “anonymous” (or at least - easier to be anonymous) than proton/tuta, but actual confidentiality of the emails was nonexistent by design.
It still possible to use Proton/Tuta completely anonymously, its no Google, but its more difficult now due to spammers abusing the services.