I agree 100% with MichaelBennett. I think the beauty of movie musicals come from seeing a film actor show off their acting skills through the music. For example, Helena Bonham Carter might not have a great singing voice, but she sure could act that SWEENEY score like no one.
Rita Moreno says something similar about being dubbed in "A Boy Like That." She says that her Anita is doing something, displaying a specific set of emotions, and the dubbed voice is doing something different that doesn't truly capture what Moreno is doing on screen.
I'm not a fan of dubbing, I agree that "sweetening" the sound is a more appropriate technique.
"Some people can thrive and bloom living life in a living room, that's perfect for some people of one hundred and five. But I at least gotta try, when I think of all the sights that I gotta see, all the places I gotta play, all the things that I gotta be at"