I have a feeling that the Rickenbacker neck bending thing is a hang-over from a couple of years in the late 60s (or thereabouts) where they used too soft a steel for the truss rods so the threads stripped when you turned them if under tension. They then switched to a harder steel and they have been fine (as much as any truss rod can be) since.

I adjusted the only two Rickenbackers I've had to look at in a standard manner without issues. But on a standard width neck (and especially the thin Ricky ones), the two rods are too close together to actually counter any significant level of twist on the neck (which was the case with the 650D I set up). If you did manage to get the fretboard flat from side to side, you ended up with a big back bow. I had to level the frets to get the action down to a reasonable level, but you had flat frets and a wonky board.

I think having the twin single-action truss rod channels weakens the necks and actually encouraged twist. I feel a single double action rod is still a much better solution on standard width necks. Sometimes it's better to dump a dubious practice, even if it is 'tradition'.