Lots of vintage frame packs were barely if ever used and turn up here and there, including the web auction site (but be careful of unreasonable shipping costs). I found a wholly unused one from way back in the 70's at a garage sale, which had been wrapped up in someone's closet all that time, and traded a half-empty quart of marine varnish for it. It probably cost $250 when originally purchased, even way back then. I've obtained several high-end vintage packs that manner, more than enough to outlast me. But that allows me to have a fully loaded up photo daypack always loaded up, in contrast to a still bigger long-haul pack with somewhat different contents, plus whatever camera I finally choose to put in there.
When California Kelty sold its rights, the resultant Korean and Chinese bait and switch products were simply awful, and straps would break on the very first outing etc. But my friend tells me this newest design looks like the real deal. He carries up to 110 lb loads, so it better be. My typical load until my late 60's at least was between 75 and 85 lbs, but sometimes up to a hundred.
But at almost 74 yrs of age now, I have to significantly lighten that. Still, a well balanced true backpack is much less strain than even a modest shoulder bag. I use those too, but for quickie convenience outings mostly involving a Fuji 6X9 RF or single lens Pentax 6X7 setups.