The Zpacks Zero's are nice packs. I had a size small but extended a bit taller, so it still had that narrow shape but it could expand if needed. It was quite spacious and I wouldn't have wanted the medium for my near SUL gearlist. A normal 'small' pack is a good size for a 6-8 lbs typical baseweight.
As with anything, there are compromises. The Zero is going to be adequately durable if you take care of it, but it's not something you'd want to skid down a talus slope on. It's a specialized tool.
I think the biggest question for you is how versatile you want your pack to be. The Zero would work nicely for the trip style you mention, but what if it's a colder weather trip where you want even more clothes or snow shoes? Or a desert trip where you're packing a lot of water? Or with a spouse/friend and you're carrying some of their gear? Or a camping centered trip where you want more luxuries? The Zero's are sweet packs, but they're quite specialized and I would normally recommend one only as part of a multi-pack quiver, or for someone who truly only does SUL/UL hikes in relatively docile conditions.
For me, I find that on a lot of trips I'm either carrying a lot of food (long trips), carrying a lot of gear (hiking with my wife) or carrying alternative transit methods (snowshoes, packraft) so my Zero hardly gets used, which is why it got sold despite being a really neat piece of gear. It was only a suitable choice on short/light solo trips, and on those trips I'm already far lighter than my average trip, so owning another pack to save even more weight on these few trips wasn't justified.
So for most hikers I'd suggest some sort of a 1.5 lbs pack with simple frame stays as a good all around pack. Something like the ULA Ohm (my favorite), HMG Windrider, GG Gorilla, MLD Exodus FS etc.