Greenguy suggesting that people like her don't exist in the industry is simply playing to the stereotypes, if they did that then the writing would be more contrived and uninspiring. Most people love to support the under dog. Plus, I know a few people similar to her who have been successful, they got by on sheer talent.
My biggest issue with McPhee is that she is not convincing as a the next big Broadway star that the show wants us to see. McPhee is talnted, but very clearly a pop singer doing Broadway tunes. Yes, I realize she studied theater, and that people can cross over, but she's not convincing as this amazing Broadway talent. And then we've got Megan Hilty who is pure Broadway. They really should have cast someone like Laura Osnes in the Karen role, or directed Megan Hilty to be terrible or something. I just don't see McPhee killing it on songs like "Let's Be Bad" the way Hilty did. Just IMO of course, but it's laughable that McPhee's character is supposed to have some quality that Hilty's character lacks because McPhee isn't able to sell that.
HumATune stated my thoughts exactly. I get that the story needs to be interesting enough but McPhee just doesn't have enough of a Broadway voice or acting ability to make me believe anyone would cast her in the lead of a Broadway musical without any prior Broadway or TV/film stardom.