In my experience Hibernate fails badly at dirty flagging and saves every field in the object rather than updating the changed properties (active record is better). I suspect that's a design decision, to avoid an object in cache being partially stale relative to the DB. But it's an problematic solution to something that didn't need to be a problem.

Hibernate does manage relationships - but that is a misfeature. It's doing the wrong thing well. The right thing is not to try to model relations as objects, but to model queries as methods. The relationships exist only in the database - they are not duplicated into the data objects.