Yes, they are simple bows out there. Is the horn bow and sinew backed bow not an innovation beyond the simpler self bow? Hunter gatherer societies developed these weapons - The Sheep Eaters/Shoshone, Hidatsa, Nez Perfe and some Paiute groups. Paiutes built incredible bows and have always been dubbed the lesser of tribes because of their very nomadic lifestyle and few possessions. The Modoc, Klamath, Hupa, Shasta built some of the most beautiful bows in North America. In general California tribe arrows are always a work of art and very intricate.
All these tribes are “ hunter gatherer societies”, yet they developed these bows. There was no need for it, the sheep eater and buffalo eating tribes did not have to developed these horn bows to be successful in their hunt. Look at the Comanche bow, very simple not much to it. Of course the horn bow folks didn’t t have Osage. My point is they sure as heck took time to develope better performing bows than what would have been needed to survive and provide for their tribe.