The Zero is not a gunbelt. It's no stiffer than any belt you can buy for the purposes of keeping your pants up.
Comparing the Wilderness 5-stitch to the newer CSM is interesting. I don't have a new 5-stitch, but if it hasn't changed in the last decade, the CSM is not thicker and not stiffer--except vertically.
The Aegis is a good example of stiff SCUBA webbing. The CSM is much more flexible in conforming to the body. As well, SCUBA webbing gets softer with use, and that can either be good (if the belt was too stiff when new), or bad. A friend was just complaining that his Carbon Tactics belt was "wearing out" and becoming too floppy. My polymer lined San Mai has a ton of wear cosmetically, but hasn't changed in stiffness.