Thanks, that was an eye-opening video.
As to your question about kites.
There have been sport kites which use battens to shape the sail.
And there have been broadseamed sail sport kites in which the sail is sewn to take a shape when wind filled.
Kitemakers today are very adept at shaping a single layer of material by using standoffs, framing and sewing techniques. I'm guessing the multi-layer technique we saw in the video would produce a very heavy sport kite.