> SQLite doesn't support functional indexing

SQLite has "Indexes On Expressions"[1] since 2015. I'm assuming functional indexing in Postgres is the same. So I think the syntax would be:

    CREATE INDEX idx_t_bar ON json_extract(data, '$.bar');

[1]: https://www.sqlite.org/expridx.html

> Also PostgreSQL has many operators[2] which makes using JSON fields easier.

This does look a little more convenient to write than SQLite's JSON syntax, but I don't see any fundamental difference here.