The "parcel of air" theory is all good and well until that parcel of air gusts, wanes, rises, sinks, sheers, or otherwise changes direction and speed.....The reason for caution turning upwind or downwind (even if that happens to be crosswind) is because that's the direction the wind is likely to gust or drop off - leaving you in the poo if you are low and slow and in a turn losing lift.
Who in the world would be low and slow and turning? Crop dusters and others who have low level endorsements and are aware of the pitfalls aside. In any case I would assume an aviator would ensure that he keeps airspeed well in hand, and not nibbling on, or close to the stall if low level. Who spends their time in manoeuvring flight below 500'? He/she may well use the "Flight Safety Foundation" recommendations for approach speeds as a basis.
Wind Conditions
The wind correction provides an additional stall margin for airspeed excursions caused by turbulence and wind shear. Depending on aircraft manufacturers and aircraft models, the wind correction is defined using different methods, such as the following:
• Half of the steady headwind component plus the entire gust value, limited to a maximum value (usually 20 knots);
• One-third of the tower-reported average wind velocity or the gust velocity, whichever is higher, limited to a maximum value (usually 15 knots); or,
• A graphical assessment based on the tower-reported wind velocity and wind angle, limited to a maximum value (usually 15 knots).
https://flightsafety.org/wp-content/...-apprspeed.pdf