I've backpacked a bit, and besides weight, there is also the space limitation. The Taurus/Winchester, Marlin, Browning take down .22s all take up space, and broken down they are still longer than the longest dimension of lightweight packs. And the ultralight packs usually are not constructed of strong enough material to support large metal objects with sharp or hard edges. Just bought my son a chinese pack for $25, 3500 with 600d material. Had looked at an MHW pack for $80, 2200 with 100d material. The 600d material can handle rubbing and poking with hard metal edges, and weighs 4x more. We have an older rogue chipmunk with a rear peep that can break down with a pocket knife, but the edges on the rear sight would need to be wrapped before placed in the pack.
It would seem to me that anyone who would want a 1# gun would benefit most from a handgun. The only benefit of the longer barrel is sight picture, but again, if you're ultralight backpacking, you're probably already used to doing more with less.