I think Carrie's problem is stage-fright. Maybe in time she can adapt to singing in front of millions (that's a lot to ask of anyone), but right now she looks like a deer in headlights.
You're right, though. She should be head & shoulders above everyone else by now.
Just FYI for comparison with Carrie, here is a photo of the new Nashville Star. Both the girl's looks and her voice are just average, in my opinion, but she is one heck of an entertainer.
And here's the difference in why Erika Jo performs so much better than Carrie -- experience. She's a high school senior, but she's been performing for over 13 years. She first performed with her father's band. Before being on NS, she fronted her own band which performed across the U.S. and internationally.