Anecdotally I've seen much bigger gains on my team's Spark jobs that use complex business logic (i.e. our own hand rolled algorithms in idiomatic Scala) compare

Anecdotally I've seen much bigger gains on my team's Spark jobs that use complex business logic (i.e. our own hand rolled algorithms in idiomatic Scala) compared to plain ETL jobs that use the vanilla Spark API, which is now very mature and optimized. GraalVM does a really impressive job with mediocre code :-)