Cause yeah I can get on board with internal frame packs and carrying meat bags instead of using a large external frame pack. At point you're shuffling weight around and it could be meat, water, food, or anything getting carried. Couple of ultra-flex trash bags and good to go.
Or do you literally mean no frame at all? Like an old Jansport daypack with two straps on a bag of nylon?
I can't image carrying any type of weight with absolutely no frame at all. I don't know how I survived school with a Jansport, other than by using textbooks as a crappy internal back panel. Even Hyperlite Gear Dyneema packs for the crazy-ultra-light hiking crowd typically have two aluminum stays that act as a frame to transfer load to the belt. Those guys skin out at barely 30#s and still have some kind of frame.
I do have a couple of the GoRuck brand backpacks that are unframed, very heavy duty, no waist belt, but I have a plastic stiffener in the one that doesn't have a plate in it because otherwise they're unformed lumps of things that poke me. I work out with a 35# plate in one pack to get ready for backpacking season over the winter, if it wasn't a steel plate that pack would a lot to carry.