I mean, the issue isn't so much that bugs exist -- like you say, that's par for the course, even among the best developers. It's about a large incidence of severe eat-your-data bugs in such a short span of time (roughly a year) in something that's quote-unquote stable and whose entire purpose is long-term data storage and retrieval.

It's even worse because unlike rsync, which synchronizes filetrees from point A to B and can be immediately confirmed to have either worked correctly or not, borg uses a bespoke storage format that's not easily verified or operated upon by standard utilities. You just have to trust it to pull the correct data out when you need it. That's a heavy burden to put on a tool, and the borg devs seem to be struggling under its weight.

Consider the standards expected of filesystem or database maintainers. borg repos are not really that different -- they're a big, opaque chunks of bytes that you expect to be able to produce specific data on demand with perfect reliability.

These types of systems don't get marked stable when they're still in primordial, eat-your-data development phases, and on the small handful of unfortunate occasions when data loss bugs sneak in, they're a) usually limited to some bizarre corner case; and b) taken extremely seriously, almost to the point of solemnity, and often result in major overhauls to a project's validation and QA routine.

If any stable filesystem or database had 4 widely-applicable database corruption bugs within a year, it'd be lights out for that project. All trust lost, reputation irreparably ruined, angry letters to a variety of mailing lists, permanently-increased scrutiny on any new projects or maintainers among the same class of projects, etc.

All I'm saying is that based on my admittedly-murky prior experience, the project's observed track record, and the high standard of care that must be met to qualify a project for storing authoritative copies of data, I'm personally not comfortable trusting borg with anything important any time soon. No one is obliged to share that evaluation, of course.