I think the point is for the zinc to sacrifice itself to the bands so the tank doesn't, and it is a slow enough process that it isn't cause for concern. The metal/metal also provides a lot of friction which you need in the doubles to keep them from slipping whereas a stage bottle hose clamp should never see any vertical forces. Also covering the screw is most important since that saves your drysuit though. Can't use nylon webbing on the doubles bands because nylon is useless when it gets wet so it would slip like no other in that situation, tubing would cause water to sit around the bands causing more oxidation to the bands. A lot of the older bands had rubber pads on them or the whole thing was dipped in what looked like plastidip. Those have fallen out of use, likely to WKPP/DIR practices standardizing away from them. Could be wrong on that, but it wouldn't surprise me.