If you need more information about how the guard waypoint is being used in this example, I have made a tutorial video showcasing its use for both infantry with and without a vehicle, though the bug is not seen fully in this instance as it is less pronounced with ground vehicles as it is with aircraft.
https://www.youtube.com/watch?v=d8qj6ILPu5E
I understand it is unlikely that something like this can be fixed without time consuming changes to the AI, but I figured I may as well shine a light on it since it is the only thing stopping the guard waypoint from being the single most useful thing in the game.
P.S if you could add the guard waypoint to Zeus so that people can experience the power of dynamic QRFs without needing people like me to make compositions for it, that would be great!