I’m not with you on trashing Marni’s voice in the original film:
https://www.youtube.com/watch?v=_SQ4ogstDVE
(I did meet her at a party once in her advanced years, however, and I will say—she was rather full of herself.)
I’ve always found her voice shrill and devoid of any character. It’s all technique. I don’t like what she did in “My Fair Lady” either. Not having Julie Andrews in that film is one of the great missed opportunities in film history.