I guess it depends what you want to do with it. I know a backpacker who'd call a trash bag an "ultralight pack."
I'm always looking to cut pack weight so I went through the same research process. I decided I wanted three pack setups, for the most flexibility:
1. An extended-range pack that could be reduced in weight for day-hunting and hauling once base camp was set up. I chose the Eberlestock J34 "Just One". It's mostly great. I pack my camp setup in the duffel which is doubly nice because not only can I cut most of my weight (and make the pack smaller) when I'm hunting, I can also do it very quickly. I don't have to set up camp right then, I can just find a likely spot and drop the duffel, so if I scout around and change my mind it's no big deal.
I carry this everywhere and leave it in the truck even if I'm not hunting with it, because it's also my hauler.
2. A "day hunting pack" that was as light as possible while still being able to carry JUST enough gear for a moderate-weather spike-out overnight, and/or a "light load" (meat bag or elk front quarter) as the first trip of a pack out until I switched to my hauler. For this, I went with the Badlands Superday which is only 3lbs 15oz (and also very quiet - better than other packs I've tried).
3. An "ultralight" pack for sunrise->sunset hunts where I know camp is nearby and especially when I need to be nimble and quiet (crawling around dark timber for elk). I went with a Mountainsmith Tour lumbar pack that's only 1lb 12oz for 9L of storage. It easily holds two water bottles or one bottle and a small spotting scope, has a compression panel for a poncho and ground pad, and some small side pockets for stuff like chapstick and windicator.
