What I heard then say on the product previous was the 4800 is simply responding to customers “asks” - everyone loves the solo, but just wanted a tad more space without the requirement to strap on lid/access bags etc. It looks to me like they delivered on that. Having the sky 5900 out there, which was the original “more features” bag they did on top of the solo, fills that gap for more space, if you like the beaver tail layout. I’ve always preferred the solo bag shape/access, so this 4800 is “perfect” in my eyes, but not being into it over some of the similar sized packs makes sense certainly.
As far as the smaller terminus - the 7000, minus the 2200 ci space for load cell, IS 4800 ci so that pack really handles like that size most of the time. 5900-2200 is 3800 ci and pretty dang small to try and pack a multi day pack camp unit when considering food. I think that’s really the main reason they haven’t made a smaller version vs larger. When you look at the weight savings/material, the big advantage the terminus line has is how much volume you get for the weight. It compresses so easy that going smaller isn’t as ideal? That’s what I see at least.