Right. There are endless posts here every year about actors and roles being in "wrong" categories, but it's all about billing (and the administration committee's determinations of when to go against billing).
Pierce may be below the title, but he's immediately below the title as "also starring" and the same type size as Midler, the title, the writers, the director and choreographer. (And Gower Champion.) It'd be hard to argue that that's "featured" billing. (Though I'm sure the producer will insist that it is, if he considers the chances better.)