I was surprised by the lukewarm responses, except for Tim's praise. I thought he did pretty good, not his best, but it was really good.I figured that maybe it's because overall, J.D. has been getting good feedback from Dave & INXS for everything he has done so far, even the stuff to rile up the other rockers, so maybe they are trying to not overly stroke his ego, so to speak.
Also, I think they have really high expectations from him and he is a serious contender, so any criticism is only going to help him get even better, keep him on his toes and not let him get "too comfortable."
If you notice, some of the other performers in the past, on not so great performances, INXS was "kind" in their remarks. It won't help them get better and I think INXS just wanted to be nice & send them on their way.