Well, I've seen plenty of videos where guys are crashing perfectly good helicopters flirting with tailwinds. So it kinda makes this "correct technique" seem as common as what we used to call "common sense", lol.
Agreed but they are often due to poor planning and power awareness or not realising they are in fact downwind.
You can fly a safe downwind approach using exactly the same technique as an into wind one - it's not a special technique never taught to pilots, it is the same technique with awareness of the differences in power requirements during the approach.
Devil, you describe an academic approach - selecting the correct decelerative attitude to maintain a constant reduction speed coupled with controlling the glidepath (approach angle) with collective. However the changing airflow over horizontal stabilisers as the rotor downwash moves off them (lower speeds) inevitably requires some cyclic corrections to be made along with the inescapable effects of flap forward (the reverse of flapback)during decel.
Most commercial and military operators wouldn't fly your slow approach way since time costs money for commercial and a slow approach makes you an easy target for military ops.