I know the famous quote. But I also know many professional ballroom dancers, and how good a couple looks is mostly determined by the man. The man drives the dance. It's his job to make his partner look good, and that means adjusting things to the skill level of his partner. A very good woman will have a much harder time making her man look good if he isn't, because she cannot backlead.

Ginger Rogers was a very good dancer. But she just isn't as good as Astaire. If you watch closely, for example, he is always perfectly positioned, Ginger, not so.

Astaire also developed the dances in parternship with Hermes Pan, who would play the female. They'd work it all out to perfection, and then bring Ginger in to teach it to her.

Also, stepping backwards is not a problem for professional dancers, and women ballroom dancers spend thousands of hours dancing in heels, so those present no special difficulty, either.

Anyone who says this has not seen an Astaire movie. Here are two routines I found in literally five seconds:

https://www.youtube.com/watch?v=IfnNwXxJeIY https://www.youtube.com/watch?v=ac6o8PXthzQ