A few years ago John McEnroe delved into controversy after being saying he thought Serena Williams was the greatest female player of all time.
Why qualify with "female"? he was asked.
Because, he claimed on the men's tour she would only be ranked 700th or so.
All hell broke lose.
I'm no expert. I believe Serena would probably rank higher, but still in three figures. I've already posted the evidence of that. And no, mixed doubles aren't mixed to bring the men's game down, they're mixed to make the match fair.
I think the better response from McEnroe might have been to ask to define "greatness" in this context. It needn't mean necessarily win against all comers regardless of sex. It might mean number of titles, time ranked number 1, impact on the sport. So in that respect his answer was unnecessarily constricted.
Personally, given that I avoid sports statistics at all costs, I can easily accept a Williams or Billie Jean King or Margaret Court (24 slams to Williams's 23) based on impact, winning record, etc as the greatest of all time.
But if McEnroe intended his answer to be the player who could best all opponents then his answer was certainly neither sexist nor inaccurate.