That was a bizarre point of view from radio. The Stylistics were very definitely male, last time I looked.US Billboard lists 25 female-based songs in the Top 100 for the year. That's 25%, including the biggest of the year for Streisand.
This counts a few male/female duos, but does not include acts like The Stylistics, which radio counted as a female sound due to the falsetto vocals.
A coincidence - I was just listening to two Stylistics songs over and over when I read your post - ‘Stone In Love With You’ and ‘Stop, Look, Listen’ - but Johnny Mathis’ versions.
I remember that when I was ten, some of my very favourite artists were Carpenters, The Stylistics, The Sweet, Diana Ross, BJ Thomas, Maureen McGovern, The Temptations, The Bee Gees and Debbie Byrne. (That was before The Bee Gees’ awful falsettos came into play).
I was definitely an easy-listening kind of ten-year-old.