He fell a really long way. I don’t believe the air makes that much of a difference. Put it this way, if he had fallen over a flat surface and there was a strong wind blowing over that surface (parallel to the surface, perpendicular to his fall), it might nudge him some, but he’d still be pretty dead. The angle of the slide certainly helps, but I still think he would have been pretty badly hurt.
But it’s never actually bothered me that much. Just pointing out that the silly nitpicking goes both ways.
On another off-topic note, I always remembered Vader holding Luke up for a moment with the Force (part-way down the shaft) before letting him continue his fall into the chute. I don’t actually think it was in the movie, but my inaccurate memory insists it was there once upon a time.