It also doesn't take into account the effects of different riders, bikes, and positions on aerodynamics. If it were necessarily the same thing to go 60 into no wind as it were to go 20 into 40kph wind no one would bother with aero gear or positions.

Then you have wind direction. Fat chance you're headed directly into the wind constantly (though I think we've all had rides that feel that way. This is all compounded by the fact that real wind changes speed and direction frequently and does not present a steady opposing force.

Most importantly, force and speed do not have a linear relationship (though force and acceleration do).