Curtis' emphasis on moviemaking as a collaborative endeavor is correct, I think. But I wonder about the phrasing of the following quote:
In his book The American Film Musical, Rick Altman suggests that Kelly owed his stardom, at least in part, to a new way musicals were cast. Beginning with the actor Joseph Coyne, and later Fred Astaire and Maurice Chevalier, directors began picking talented dancers with little formal vocal training for their romantic leads. Kelly didn't talk his songs like Rex Harrison, or croak them like Mickey Rooney, but his voice could be shaky.
It's true that these gentlemen had little formal vocal training, but I'm not sure that there was a time when directors suddenly started "picking " such performers. Musical comedy stars in general had a specialty – singing or dancing – and although they usually did both, generally their expertise in one department was superior to the other. Astaire and Kelly were hired as dancers first, singers after, and directors didn't necessarily have much to do with their being contracted to the studios in any case. And very early on, both men were choosing their directors or approving them. Harrison didn't star in any musicals until quite late in his career. I can't help thinking this quote represents director-centric thinking that can often be misleading when discussing Hollywood, especially old Hollywood.