I think from a 1950s sensibility, Maureen O'Hara was too strong, too forward, too in-your-face ... a gorgeous beauty, and yes, she could have sung it well, but not right for Anna, who needs to be strong, but also is a "lady" with a more genteel demeanor to go against the King of Siam. It's not "clash of the titans," it's more beauty and the beast.
And while Kerr was enough of an actress to play barmaids, nuns, tarts, or ladies ... O'Hara wasn't quite as much of a chameleon. She was a good actress and a big movie star ... but not right for Anna.
Today, they would probably cast O'Hara anyway because she could sing it even if she wasn't right for the part. Back then, they would get the casting right, first and foremost, then dub the singing to make it work, if needed. They even dubbed people who could sing (like Rita Moreno in WSS for A Boy Like That, because her own voice wasn't right for the song). There is no "attention to detail" like that today. I miss it.
"Jaws is the Citizen Kane of movies."
blocked: logan2, Diamonds3, Hamilton22