The only thing I can find on Scala with "sealed" is for exhaustive pattern-matching on types, which 1) broadly matches Java, and 2) has nothing to do with data-

The only thing I can find on Scala with "sealed" is for exhaustive pattern-matching on types, which 1) broadly matches Java, and 2) has nothing to do with data-only objects at all. Sealing and methods are entirely orthogonal.