And the load on its sheets is enormous. Oh boy can it cause a problem if anyone makes a mistake handling it! Now imagine the load from the kites proposed. I wonder if that is even feasible with today’s materials.
Edit: did some reading around. So it seems at current level the system can be used as a supplementary propulsion saving some fuel. Ahoy, mates, we are back and our sails are higher than ever!
When it comes to material stresses the sails can always be scaled down, but off the top of my head kevlar and zylon would be good candidates for getting the biggest, toughest sail in an economic fashion.
If you want to go down a related rabbit hole take a look at the sails used in regattas. The technology and money that goes into them is ridiculous.