In terms of number of functions PostGIS is still the leader, but for analytical functions (spatial relationships, distances, etc) having those in place in these systems is important. DuckDB started this but this has a spatial focused engine. You can use the two together, PostGIS for transactional processing and queries, and then SedonaDB for processing and data prep.
A combination of tools makes a lot of sense here especially as the data starts to grow.
Postgres made gigantic leaps in recent years - both in performance and feature-set. I don't think ever comparing the new contenders with daddy is fair. But then there are the DuckDB advocates who claim it pioneered spatial, which is so much not true.
Postgres is amazing system, which is also available free. We don;t have too many of these, and too many aging that well.
My bet is most of actually useful spatial ST_ functions are not implemented in this one, as they are not in the DuckDB offering.