So in a really important sense, these creators (and these companies that had third party integrations) were (are) using Patreon.com as an identity server. But not just an identity server. It doesn't just serve the identity of patrons, but their status as patrons. That's part of what makes it "audience relationship management".
If your supposed Patreon competitor does not support doing that, well, you're certainly not going to seduce all of the creators clinging to the sinking wreck of Patreon's API into abandoning ship on your account, are you?