It's not so much about size but about usage pattern.
If your workloads require fast writes and reads, SQLite will probably work fine.
If you're looking to run analytic, columnar queries (which tend to involve a lot of aggregation and joins on a few columns (say less than 50) at a time), then DuckDB is way more optimized.
Oversimplifying, Sqlite is more OLTP and DuckDB is more OLAP.
If your workloads require fast writes and reads, SQLite will probably work fine.
If you're looking to run analytic, columnar queries (which tend to involve a lot of aggregation and joins on a few columns (say less than 50) at a time), then DuckDB is way more optimized.
Oversimplifying, Sqlite is more OLTP and DuckDB is more OLAP.