It is optimized for analytic workloads (default in-mem columnar layout), whereas PG and sqlite are OLTP DBs. It's going to be insanely faster for those use cases.
DuckDB is an in process OLAP, I’ve been using it a lot, and I am keen to use Polars but DuckDB seemings to be flying for me.
It’s much more similar to cleaned up Spark syntax vs Pandas’ strange API.