Technically, i suppose that you are correct. And i really don't know if i would have handled things too much differently. Or maybe i would have, depending on how much time i had available. But dis-inviting someone to a gig can be pretty cold, at the very least. Have seen this in another band that i sometimes guest in. If the whistle player cannot make things work as a duo, some other alternatives would be: find a temporary third player, or, permanently replace the whistle player. It would be difficult to diplomatically explain to the whistle player that yes, you are good enough if there are enough players to cover you up/cover for you, but not good enough if the audience can really hear you.