Those are pertinent questions.
In fact I researched about those since I posted this problem and have come to some conclusions,
- Open-source alternatives for Patreon [1] [2] have done poorly and have been abandoned; I think its largely because those who use Patreon are non-technical users and they weren't looking for a self-hosted alternative.
- Patreon has become synonymous with donations due to YouTubers, That even those who are capable of self-hosting (or) creating their own payment host is choosing to use Patreon instead for its brand.
That said, The problems I mentioned and bad reviews of Patreon on trustpilot suggest that there could a need-gap for an alternative. Perhaps, Another Patreon is what could address that instead of a self-hosted one.
I'm planning on building an on-premise payment host as an alternative for Gumroad instead - /problems/399 , As I think it could address problems with Gumroad better.