Yes as a raft designer myself, there is a line where ultralight function and safety margins meet. If I need a packraft to haul >100-lbs of meat plus myself and kit, I would have at least 2 air chambers (not one like most packrafts) and made with a minimum of 420D dual-coated fabric. The trade off to this minimal viable product is the argument of pack weight. All the brands you've mentioned aren't hunting-specific designs, so there are safety margins they aren't even aware of in our world and their designs reflect their target user group. So, some guys are making it work with the larger packrafts like Alpacka started years ago, but they aren't ideal for hunting application in sketchy mountain tributaries. In many remote places you need flotation, which requires air pressure which requires heavier fabric and added weight for 2 air chambers and air valves.
What Stikine has done is created a heavier denier packraft and perhaps to stay competitive in weight savings chose the single side coated fabric. This is all just a speculation from a designers perspective.
In answer to your question about advertised weight capacities, that's a great one. There is no official guidance for manufacturers to set weight capacities; however I set my designs' "weight capacity" to provide buoyancy of 50% hull depth above and below the waterline. With packrafts that 50% draft don't mean shit if you're heavily loaded in a small craft with wave heights larger than your tubes, as that waterline fluctuating up and down alongside a 13" tube diam doesn't take much to take on water or provide sufficient pucker factor. The margin of error for hunting packrafts, IMO, is worth the extra pack weight of a more robust design specific to your expected weight capacity demand.