You got it wrong, you are not paying for the Sync service, you are contributing to Logseq “community fund” and as a reward they let you try beta or alpha features (depending on how much you donate), you are supposed to test it, they are supposed to consider your feedbacks and only later Sync will become a paid service.
The whole Logseq is in beta, not only Sync. We are not supposed to use it in production until version 1.0 is released. It’s just that Logseq is already good enough that we all want to use it in production. But the truth is that we are early adopters helping with the development of a future product.
Is Logseq taking too much time to release a 1.0? Maybe, maybe not: it has been ~3 years since the first release and ~2 years since a team has been put together. 2-3 years is already the time most commercial proprietary software need to be launched anyway.
So the way I see it, the FOSS model is giving use the priviledge to try some software while it is being developed and to contribute to it.
There is still a chance Logseq team will fail and Logseq will be abandoned but it doesn’t seem the case at the moment, they have a plan, it’s a long term one, only time will tell if they were right investing so much time, particularly the last year on the DB version.