This isn't true. It's not true for normal people who have substantial shooting time behind their favored gun, and it's not true for the elite.
Maybe there are some freakishly fast single action guys who do trick shooting who are faster with a single action revolver than most people are with a double action revolver, but none of the cowboy gun shooters can come close to the freakishly fast Jerry Miculek .. especially if any reloading is required. Jerry Miculek speed shooting record setting video
Miculek is a space alien, no other explanation for what he can do.
Bob Munden would put him to shame, guy could split a card on edge with his single action. He also could fire two shots a break two balloons so fast you never heard but one shot, or saw it either. Bob is dead now but man he never missed Could shoot aspirins from nail heads leaving the nail untouched.
https://www.youtube.com/watch?v=IUHZX7C_73o
https://www.youtube.com/watch?v=eWy1AiJ8lyE
A couple cowboy shooters who are pretty quick.