I think people took "falter" to mean "flubbed the lyrics". That is not what I was referring to. I think flubbing the lyrics (once) is pretty insignificant. What I was referring to when I said "falter" was failing to do what I said before: Making the song they're singing something important, current, vital, relevant, exciting to listen to, etc. Michael Johns' performances started out great, and then started going dull for us. He just wasn't doing anything special anymore to make us want to buy his albums or care if he wins or not. Same with Amanda (who flattened out pretty quickly and never was able to recreate the excitement we felt for her during the auditions/Hollywood Week) and eventually Carly.
Brooke, actually, was the exception: She continued to provide vital performances, but she actually went overboard with technical faults... she showed that she was not ready for prime-time by flubbing the lyrics on-stage for a second time in just a handful of performances.
They all can't be superstars... well they can be, but they're not. Michael Johns seemed like he could have been, but didn't live up to that initial promise I saw in him. With someone like David Archuleta, I believe he could grow into a superstar -- well, maybe not, but that's the point: He's young enough that we really don't know what he could become at this point. My impression is that Michael Johns has reached his full capability, and it just isn't good enough for him to be a superstar. (But he was off by not much, mind you.)
Incidentally, I think David Cook hasn't hit his full capability. Good thing too: I don't think he's as good, today, as Chris Daughtry is, or was while he was on AI, for that matter. However, I think David Cook could end up being better than Chris Daughtry. I have seen nothing to indicate that he couldn't... he keeps getting better.