The other famous female french swimmer was the total opposite in stroke style.
smooth versus swimger as swim smooth would call it.
I call it the skippybal style. Bouncing from one side catch right into the other side.
This bounce technique is very widespread. Even Sun Yang at 0.25 speed slowmo reminds me of footage of the first man walking on the moon.
Bouncing forward and up from their supprot points.
In Sun Yang case its the fall on one side of the body, let it reach it deepest point and bounce, catch and kick to the otherside.
Its almost imposibble to have only forces working straight backward, just like walking on the moon. This is the way to recycle most of the diverted energy.
Try it and watch on 1/4 normal speed. His bounce is mild and mainly on his nonbreathing side.
Thats why I like to swim above a minimal stroke rate. Skippybals have a cretain preferred bounce rate.
2BK is the ideal bounce kick, or 6bk with a strong 2Bin it.
Skippyball swimming is fun, but you can easily take it too far, just concentrating on the bounce and not on the forward progress.
Popov also did a lot of skippyball swimming