The thing with Idina is that I feel like her only problem is that she gets nervous very easily which affects her singing and make her speed up. I think she has a fantastic voice and I loved her defying gravity from Wicked.
https://www.youtube.com/watch?v=MslDnwerQRA
I really think she was just hella nervous (I mean so many people on stage for the oscars was pretty nervous)... you can tell she was also disappointed with the way she pulled off the last note. =(
https://www.youtube.com/watch?v=4dPim-NN3mQ
^ she looked really relaxed there, maybe because she had someone with her, but she sang that perfectly there!