Volcana-the King final Evert was referring to wasn't a slam. It was Philadelphia in 1978.
To be considered for an all-time #1 you have to have something others don't. Using that logic, only a few are "contenders' for the top.
In order by date played.
Lenglen- dominant(lost only once after the age of 14), won lots of majors,including 6 Wimbledons.
Wills-again dominant(won about 180 matches straight and undefeated for nearly 7 years. If the Aussie isn't counted, she has the most major event wins.
Court-has the most slams(24)-though 12 of those are in the weakest, the Aussie. And a grand slam, in 1970.
Evert-Has lots of slams(18), record 13 years straight as a winner in majors(1974-86)-consistency her unique advantage.
Navratilova-Has lots of slams(18)-most dominant season among those after World War II(losing one match in 1983)-strongest case is she has the most titles(9) at the most important event, Wimbledon.
Graf-has the most slams outside Court(22). Grand slam in 1988.
Only one with 4 wins in each slam.
Outside those 6 no "expert" has ever chosen another candidate. Personally, I think Evert's case is the weakest of the 6, but if consistency was the only criteria, she would be #1.
This excludes those NEAR the top who for one reason or another have gaps or less titles. These women are often in an-time top ten, but you'll never see them listed at the top.
Connolly-won 9 straight slams entered,including a 1953 grand slam. Simply had too short a career to(ended in a horseriding accident) move up. Before Court came along in the 1960's, she was always #3 on all-time lists. Big question mark for what might have been.
King-has lots of slams(13?) but is clearly behind Court, Evert, Martina, etc. Only has 1 slam on clay, her weakest surface. Missed a chance at a grand slam in 1972 when she didn't play the Aussie.
Seles-has won lots of slams(9), may add to others, but without a Wimbledon title on her weakest surface, she can't move up. Of course her stabbing puts a big question mark on what might have been.