My take on this is:
When i'm out hunting I'm intending on harvesting something. So...I want to carry a pack so that i'm prepared for the first trip back to the truck (with meat/antlers etc). The last thing I want to do is to make a trip to the truck just to get a pack for the packout. No reason for extra miles on the tired feet.
I have used the KUIU Ultra 1800 for the last 3 seasons and love the pack. It's very light and worked well hauling elk quarters, whole deer in one trip etc. It's comfortable for a day pack...the only time it's "ackward" is crawling with it on during a stalk. I usually drop the pack at that point.
One BIG consideration in my mind is how much more comfortable it is to attach bow or rifle to the pack for carrying it. There are good options out there for quick release (I use the stone glacier rifle sling, modified...and the kuiu bow holder). Without a frame pack carrying a gun is uncomfortable.
For scouting, a frameless pack is a good option IMO.