No discussing mystery ranch frames. I did look at the Kuiu pack and did like those. Might go back and research those a little more.
my best advice is no need to research kuiu… nothing against kuiu, I own a lot of their stuff, and their rain gear is the best in the biz, but packs aren't their thing. without sounding like i'm bashing them, i'll just leave it as I have been down that road, and would pick a pop up for hauling weight over a kuiu frame every time.
their full size frame is of course more capable than the pop up. Mystery ranch makes great packs. i'm in the market for another full size pack (4000ish CI) and i'm torn between a kifaru and a mystery ranch.... tough decision so far.
in the past 5 years I have owned horn hunter, kuiu, EXO, and Mystery ranch.... mystery ranch has been my favorite. I hauled one bull out with a kifaru, and it was nice... not a stand alone, but not worse than the EXO or MR.... it was not my pack, so probably not ideally set up for me (but obviously close) i'm kinda leaning that way, but I have little real world experience with them, and they have an almost overwhelming lineup.
packs are expensive, and I look at them like optics, not a good category to go outside of the tried and true, and well liked. the packs I would consider are kifaru, EXO, mystery ranch, and stone glacier (may consider seek outside some day, but would need to at least handle and try one on first) besides them, I just am not considering.... it's a high dollar item, and a very important item.... either buy a nice pack, or waste a bunch of money in the upgrading process... if you wear packs a lot, and rely on them, you will eventually end up with a high end pack, cheaper to buy one out of the gate and save a bunch of money.
of course i like to learn hard lessons, but i have got to the point of knowing the importance of a good pack now, and there is no going backwards.
i did the same with optics, wasted a ton of money over the years upgrading my glass, to ultimately end up with 2 pairs of swaros.
stick to your initial train of thought, Mystery Ranch will serve you well... if not mystery ranch, than kifaru, EXO, or stone glacier.... or you will eventually be upgrading, and the pack you are upgrading won't be worth selling. good packs hold their value, the rest don't.