To your logic I would add that the heavier of your two considered base weights is going to be lighter than average among thru-hikers. And FWIW, the ULA Circuit is my favorite pack now. Heavier than some, but relatively light, has sort of "just the features I want" and you don't pay a weight hit for those that you (or at least I) don't want. For example, when I was using a Gossamer Gear pack, I would add to the weight with add-on waist belt pouches, that were occasionally a hassle in that they wanted to slide off the waist belt. Given the added durability (miles you can hike in it) and I prefer the ULAs now.

After the equivalent of about one thru-hike each, two different GG Mariposa Plus packs were not useable for much more than day hikes, but I think you can easily get two full thru-hikes worth of use out of a Circuit, and likely more. My hiking partner on the AT replaced his ULA as I recall after putting about 5000 miles on it.

I don't mean to say that makes ULA "best" for everyone. My experience on the PCT however suggests that it's probably the most common pack brand among PCT distance hikers, or at least it was.
Brian Lewis