You are right, for multiple tables, we'd have two sequences per table, and the relay should be aware of those. So a full-fledged transactional outbox approach would be a better fit if we have multiple tables and want to decouple the relay from the database structure.

There's another limitation of a simplified approach - the original table should be append-only, e.g. event-like. In case we update or remove data from the table, the simplified approach also won't work.