It seems to me that the point has been proven in the video. The open-diff 2wd Xterra was pushed up the ramp untill the tire was about to lift... At that point it spun. Then when he put it in 4wd(not shown in the video) and went another couple of inches up the ramp the tire was OFF the ground... Only THEN(when it came to the LAST couple of inches) did the drooped tire stop providing enough traction to drive the X up the ramp farther.

Also note that the revolver started to open as soon as he started up the ramp. The other side was never unfolded. If it looks like that in the video it's an illusion.

Bottom line is that too many guys have posted real world experiance with the revolvers that like them. And even a video that PROVES their point.
Others are posting regurgitated info.(with no personal experiance)

If what the naysayers is correct then in that video the tire SHOULD have started to spin as soon as the shackle started to unfold. That didn't happen. End of story.

Maybe it would be clearer if mmniac did the same thing. Only this time with tape or spray paint to mark the spot where the tire spun. Then secrure the shackle so it can not unfold, do the drive up the ramp again, then mark the spot were the tire spins.
I think you'd see a remarkable difference in how far up the ramp the X will go.