Carrie could have also stretched by doing this production in a small regional or community theatre until she learned how to act.
She plays with the big fish in the big pond, then she better be able to take the big criticism that comes with that level.
And I wouldn't have done Sound of Music at all, as I know I couldn't do what it requires.
And I'm tired of people using, "I highly doubt anyone complaining could have done the job better yourself...." as a passive aggressive smack down. Some of us have standards. I'll say it again: Audra Macdonald, Christian Borle and Laura Benanti were ALL in the same live TV performance. They were fabulous. All are Tony Award winners, who were properly trained to their levels. They have standards too, for the quality of their own work and what they are willing to put out.
The problem is that none of the three performers you mentioned would have been a draw to anyone outside of those who experience Broadway theater. Out here in middle America we are not exposed to these people. I had never heard of any of them. They do not perform where I would have an opportunity to see them.
This show was televised, not just a stage performance, and they needed to appeal to more than theater fans. My twenty-something year old daughters were drawn to this because of Carrie Underwood. They are probably not the only ones who would not have watched to just to see the performers you mentioned.