Polars is much more useful if you’re doing complex transformations instead of basic ETL.
Something under appreciated about polars is how easy it is to build a plugin. I recently took a rust crate that reimplemented the h3 geospatial coordinate system, exposed it at as a polars plugin and achieved performance 5X faster than the DuckDB version.
With knowing 0 rust and some help from AI it only took me 2ish days - I can’t imagine doing this in C++ (DuckDB).