Each to their own...
But in my eyes it does not matter how far "out" the water is, as if you get knocked out, you will drown anyways, quite fast and noone can help you.
Most often not even if friends are out too, as they wont be able to react.
As we never have many or any beachgoers in our country, when we are out, it doesnt matter - there is noone to help your, and even if, they wont have a chance to save you.
So if wind is onshore or sideon, I dont worry one bit being out alone - and have been doing this since 1978 (windsurfing before kitesurfing).
Only in tricky spots where you might drift over the "last stop" and away in the deep ocean, I dont kite alone far out, only close to the shore