I have not worked with Spark, but I have used Athena/Trino and BigQuery extensively.

For me I don't really understand the hype around Polars, other than that it fixes some annoying issues with the Pandas API by sacrificing backwards compatibility.

With a single node engine you have a ceiling how good it can get.

With Spark/Athena/BigQuery the sky is the limit. It is such a freedom to not be limited by available RAM or CPU. They just scale to what they need. Some queryies squeeze in CPU-days in just a few minutes.