Also, if the wind is giving -5watt readings, and you're putting up +5watts to hold position, it still means YOU need to generate +5 watts, not zero watts.

The overall system balance might be zero, but the rider still must produce net positive power to hold that trackstand, since he doesn't get to store the power that the wind produces to push him back. That's the point I'm making.

You could have a NFL linebacker push me backwards on a bike with -400watts for 5 seconds, and it is absolutely not true that I will then require production of zero watts to get back to the place I started, even if by your perfect theoretical system, -400 watts for 5 seconds from the backwards mvmt + 400watts 5 seconds equivalent forward = zero power overall measured by a powermeter that can record negative power. I still am produce net positive power at the pedals.