The truth is, it was not her voice alone. Holland-Dozier-Holland's writing, producing and in Diane's case COACHING, along with Mary and Florence's expert harmonies, the Funk Brothers and Berry Gordy's acute business sense combine with Al Abrams PR skills, Barney Ales sales skills and a host of other unsung Motown personnel (shout outs to Maxine Powell, Cholly Atkins, Maurice King, Gil Askey, etc,etc etc.) are all responsible for the Supremes having so many hits!
As much as I love all the Supremes and their God-given abilities, we must remember that in interviews the writers of 'Where Did Our Love Go' mention that they had worked out sophisticated harmonies for Mary and Florence to sing. Even with coaching, Mary & Florence were having significant difficulties mastering those harmonies. So much so that the very basic, simplified harmonies used on the record were created as a compromise just in order to get the song recorde
So where is it written that they had difficult times her mono that’s absolutely ridiculous .