Mastbender said..
You're forgetting about the extra strength and endurance it takes to balance when up on the foil.
Why do you think it takes more strength and endurance to balance up on a foil? Do you have experience or are you assuming?
Certainly riding on a kite foil is physically effortless, although it can be kind of terrifying and frustrating at times. The crashes hurt. If you're working really physically hard then you're doing it wrong. The physical effort comes from all the crashing and restarting.
From a kiting perspective you're not actually "balancing up on the foil". You're actually riding the wings. The mast is just a connector between you and the board. The leverage and wobbliness you would expect don't really come into play until you're so far gone you crash ... or carve a mega turn ... then crash.