Nobody has yet mentioned Kinetic Energy, the energy of movement. Equal to half x Masss x V squared. This is relative to your frame of reference.
With reference to the ground (which is the thing you are most likely to hit), a helo travelling at 30 kt in nil wind has energy related to 30 squared, or 900 somethings of energy. When it is doing 30 kt into a 30 kt headwind, it has zero groundspeed, and zero kinetic energy - it can't hit anything, so it can't be damaged by that energy.
If it is doing 30 knots with a 30 kt downwind, i.e. 60 kt groundspeed, the KE is related to 60 squared, or 3600 somethings of energy - seriously bigger than before, and a lot more energy to dissipate if it wants to avoid hitting something.
So, we watch as the chopper hovers into the 30 kt wind. Zero KE. We watch it start a turn out of the wind, and if it goes slowly, we see it fly crosswind at about 30 kt groundspeed, and eventually downwind at 60 kt groundspeed.
Where did the extra 3600 units of energy come from to do this? Did it extract the energy from the airflow? Did the temperature of the airflow decrease to supply the energy? Did it move slower, having given up some of it's "oomph"? No, and no. It got hotter (from being whacked by the rotor blades) and it moved faster, because the blades ADDED energy to the airflow. However, if it did somehow extract energy from the airflow, how does it "give it back" when it turns back into wind?
From practical experience gained over 35 years and 12,000 hours of flying, mostly helicopters at very low level, it sure as heck seems that the energy has to come from the engine. If you don't have plenty of power, you don't turn downwind. And the IAS drops off the clock, too. So, any turn out of a strong wind is gradual, and accompanied by a power increase, and do it slowly to allow the aircraft time to build up the KE.
Turn back into wind, and lower the power.
Yes, most of the manoeuvering is done with reference to ground features - powerline inspections require that. But once the turn out of wind is commenced, it is not relative to the ground features - we are not trying to follow a road or such, we are just trying to hold height, hold airspeed, and NOT fall from the sky.
When the speed of the air and the speed of the aircraft are similar, the theories of parcels of air don't seem to work. The paper aeroplane doing slow circles in a train moving at any speed, is actually moving backwards relative to the earth. Any helicopter pilot who does that at low level on a regular basis is inviting a call from his maker.