Indeed it's hard to say much here without a good sense for your expected base weight (and to some degree associated bulk of gear) --= it's hard to comment about any particular pack lacking that.

I.e., ideally you don't just want to select your tent, sleeping bag, and pad --- in a perfect world you would pick out *every* little thing and list all of that and sum the weights. With that in hand it's easier to comment on the suitability of a particular pack.

When do you plan to start (what month, ideally what part of the month)? Starting from Springer (or approach trail) in Georgia and heading North? The fact that you mention a 6 month trip suggests to me that you might not be thinking of pushing the boundaries with minimal/lightest gear (?). Or maybe that just means that you're prudently setting aside 6 months and it doesn't relate.

The Exped might be a great choice if you're starting early; or it might be overkill --- R-value of 4.9, weighs 31 or 39 oz depending on which size you get. A thermarest Neoair xlite weighs 12 oz in size regular, with R-value of 3.2. If you're starting in early March (or earlier), beef up the thermarest with a Gossamer Gear thinlight pad and still save a lot of weight --- and you can mail the thinlight home when you no longer need/want it.

WM Summerlite is an excellent choice, so long as you're not starting too early. You might be on the cold side to start with. I personally am not a fan of silk liners. If you want a bit more warmth, ask the WM folks to overstuff your bag --- that's a much more efficient use of weight and less of a hassle. Starting out you might want to wear some puffy clothes inside the bag on colder nights. Or start with a 20F bag and swap to the Summerlite after, say, the Smokies. Hard to be specific here, lots of variables. But I have a Summerlite; it's a wonderful bag.

Big Agnes Fly Creek UL 2 --- are you hiking solo, or with a partner? That's not a bad weight if you really need and want a double-walled two person tent --- tt lists at about 42 oz. If you use trekking poles, a lightheart solo is 27 oz, and is still effectively double walled, and IMO has plenty of space for a solo hiker. If single walled is okay for you, you can get a two-person tent for less oz; for example, the Tarptent Squall II is listed at 34 oz. One key question to ask yourself is how often you anticipate sleeping in shelters. The more often you do, the more you might skimp on tent comfort in favor of carried weight.

Whatever your baseweight I don't suggest that you start a first thru-hike with a truly frameless pack unless you have some experience using a frameless pack already. So of the ones listed, the Gorilla might be best --- with the huge caveat that I don't think you can yet know if any of those are reasonable candidates for you.

If I had to pick a sort of "one size fits most" pack for the generic thru-hiker it might be the ULA Catalyst. Or the ULA Circuit (which is what I use) if you know that your gear will fit in that. But as others have said, figure out the other stuff first, to include all of the "various and sundry" that can add up to a lot, and the *complete* list of clothing to be carried.