why don't you like that? The non rigid design and roll top opening are the exact reason I want the lightning lol!
The lack of frame is a problem because it compromises the carrying comfort when loaded. If you can exercise self restraint in overstuffing / overweighing it's not so much an issue, but from personal experience 14kg is about the limit to my pack. Above that weight and it starts to distort the back panel, and the weight transfer isn't so good.
I would think a single stay such as on the Thunder would give the rigidity needed for effective weight transfer onto the hips, for minimal weight.
As for the roll top, well yes it's lighter, but it's also a pain in behind hinderance in use - the long 'tube' of the rolled section just gets in the way when rooting around in the bag. I've also had water ingress from standing water in the rolls.
Golite went bust AFAIK and I don't think you can get it anymore.
On the plus sides, the dyneema nylon ripstop fabric is amazing. I've not babied it at all and there's practically zero wear. It certainly suggests 1000d 'ballistic nylon' etc bags are all just overengineered marketing. I would be 100% comfortable buying another UL bag or recommending one.