No you are not wasting your time. You supported your wife and showed support, that is never a waste. You did not allow JWs to spout self righteous nonsense they need to be challenged. You did not enable their bad behaviour.
Trust me whilst a JW I was challenged several times. I never forgot a single one of those conversations, I remembered the words and the passion and they stuck in a way positive encounters did not. Who knows what long term effect your words will have but be sure they have had an impact.