About kites being valid contenders: anything wind powered and in permanent contact with the water qualifies. A wing powered ekranoplane with a submersed board qualifies.

About Hydroptere: its merit is its ability to sail offshore with minimal changes. A lot of weight could be saved if it was dedicated only to the outright record.

About kites being less energy eficient: there should be a separate record for energy eficiency (boat speed/wind speed) because improvements in this area go beyond sailing, they are important for the future of our planet and species.

There's energy to be tapped everywhere, but we can only use a limited quantity due to heat resulting from ineficient use. If we don't learn how to use it more eficiently, the heat may actually burn the planet. Climate change and greenhouse effect are nothing in comparison.

In other words, energy efficiency is -or will soon be- the main limitation for human development. One day it will be one of the reasons to work outside the planet.