I would think David Foster's opinion ("Katharine has a great future" if memory serves) should count for a lot.
I think all three judges have a hard time not playing the original artists' version in their head while evaluating the person in front of them. I think the look on Katharine's face said it all when Simon told her she wasn't Whitney Houston. She knows she's not, nor was she trying to be. Sometimes we need to remind the judges to limit their comments to something constructive for the contestant that can actually help them improve their future performances.
The thing that is weird about her is that whenever they show her in practice with whoever the guest judge is she is bouncy and fun and shows a ton of personality. Then she gets on stage and it's like she is doing a character or acting like she thinks and Idol should act.
If bubbly, fun practice Katherine came to the stage on Tuesday nights she would have many more fans, IMO.