My read is that levkk is conflating concurrency with "real production apps" and this whole thread is starting to surface that "real production apps" and "high concurrency" are not measuring the same thing at all.

Sqlite is used in real production apps more than any other database.

Sqlite is also weak at any sort of write concurrency.

Both can be true.

Why doesn’t each of your users have a SQLite database writing up to a main?

You can have as many as you want - and one is often plenty.