A data-point:
I use a Shimano steel Q/R on a 198x Ishiwata noname frame with 1010 style Shimano dropouts.
I'm not Marty Nothstein but I'm a big boy who rids a couple of steep hills.
During the year that I've used this bike, I've had problems with slippage twice. I'd have to classify them as "pilot error" or at least "user inattention."
Fairly recently I learned that a Q/R is properly tightening if one begins to feel resistance when the lever is at 90-degrees to the plane of the frame. Before learning that rule of thumb, I set my Q/R looser than that. When I'm inattentive, I think I still do. The bike in question is a flip-flop and I actually do use both sides and have multiple opportunities to be inattentive.
When I follow the rule of thumb the wheel doesn't slip.
Richard Booth ...on a perfect Friday afternoon for a fixed 25 from... Elsah, Illinois