Yeah I don't think he's advocating riding the tail all the way around the turn :D It does look to me like the top skiers, as they pass the buoy at short lines, are pushing into the back foot to rapidly change the ski angle and in a sense "stop" their downcourse speed, then immediately getting back into a forward/balanced weight position.
Consider this piece from Denali GUT 101: "In order for a skier to complete a pass within the constraints of the slalom course at the 10.25-meter line, the variance in down-course speed is huge! They are traveling significantly faster than the boat in the down-course direction from CL to the buoy, and much slower from the buoy back into to CL."
The physics of being tied to the rope dictate that in order to get around a buoy at 41off then be back at center line with a tight rope, the skier must drastically reduce their speed at some point before getting back to CL.
In a race car, the more speed you can carry through the corner the better (generally speaking), so that they can finish the lap with a greater total average speed than other cars. But skiers ultimately can't go through the course any faster than the timing of the boat, so every person who runs the pass has roughly the same average total speed through the course. [edited following @brettmainer's corrections below]
I think @A_B's comment is insightful: how do you stop if you're about to hit the dock? You slam the back foot. Whether that's the best way to create deceleration within the many other considerations of running the course, I have no idea lol, but at least in isolation, digging in the tail is an effective way to slow down, and slowing down is necessary to run short lines.
Going off the GUT theory, my understanding of the Denali approach, and I could be way wrong here, is to allow the ski to slide, like a rally car on dirt drifting around a corner, so that the ski is starting to point back into the course and scrub speed, even while still traveling outbound (due to the swing of maintaining rope connection/load even as the ski unloads), so then at the finish of the turn, there isn't as much a need for immediate drastic loss of speed after the buoy. @AdamCord?