I think the issue with a guy like Stowers is can he have success getting infrequent at bats as a PH/bench guy?
As for sending Mayo/Cowser/Holliday down, at some point as these guys age/mature/prove that the minor leagues are pointless for them, we are going to have to eventually rip the bandaid off with stop gaps/decent but not very good players like O'Hearn, Mateo, and Urias.