Whenever the topic of disc brakes come up, there are lots of mentions of "better stopping power" and "better modulation"; it's almost like reading wives' tale from Harley riders about endo'ing if you use your front brake!
But here's a video of two VERY FAST and equally skilled riders descending on a VERY technical road with avg gradient almost 9%, so both are riding their brakes in the steeper part (later half of the video). The lead rider is on a disc bike, the trailing rider (the one filming) is on a rim brake bike. As you can see, there is litterally nothing between them. The squealing you hear later in the video is from the brakes of the lead rider. These guys got KOM (despite making a mistake) on this filming segment so they were railing all out. And in case anyone is wondering, the trailing rider's is on a non-aero bike. Granted this was in dry condition, and if in wet, then the advantage would be just slightly more for the disc guy, but let's be honest here if it was wet nobody would be riding like this.