I can't comment on the Kuiu, though I love their camo, but the MR is a flagship pack. I have the Sawtooth and it is outstanding. Personally I would lean in on the MR. Their customer service is also outstanding.Like all new hunters, I'm eyeball deep in pack buying information and opinions. So why not add some more.
Assuming the same price, would you buy a new Kuiu Icon/Ultra or a used Mystery Ranch? Looking at the Metcalf or similar size pack.
I would suggest to get on YouTube and watch the backpack torture test that Gohunt does. They use several pack manufacturers including two that you are discussing. IMO I would go with the mystery ranch.
Can't really call that one a test, more of which one won't break if it gets blown up. They didn't even try them on lolThat video is one of the most ridiculous things I have ever seen someone put out on YouTube. That single video made me think those GoHunt guys are a bunch of idiots.