my thoughts are that the review was more disparaging about the songs she sang rather than her specific performance on the songs. yes it mentions that she isn't a highly distinguished vocalist. but it really sort of slams here MOR pablum that she was using. Odds are the reviewer didn't realize that the song list was frustratingly similar to the final Sup shows

Everybody gets to go to the moon/corner of the sky
Midnight Dancer [[replacing Let Yourself Go)
Dialog
Supremes medley - come see, happening, reflections
The way we were
Sup medley - you keep me hangin on, where did our love go, baby love, love child, stop
Stoned Love
Driving wheel
Can't take my eyes/quiet nights
You're what's missing
I love a warm summer night
red hot
song for you/how lucky
Someday we'll be together

Frankly this show format wasn't all that inspired or exciting when the Supremes did it. so to pull out all of these old orchestra charts really is pathetic. Sure the first medley of Sup hits where she just sings the backing parts was cute. But the rest really is poor. Instead of another sup medley, she should have pulled Don't Let My Teardrops or You Are Heart of me. at least do some of HER songs from the Sups era