KS Ultralight looks awesome, as do the other custom options.
If you want something from a big brand, I came recently upon this pack called the Black Diamond Nitro 26.
It’s 24L in S/M, and 26L in M/L. I don’t know if it’s light enough for SUL purposes. But for a normal pack it is light, while it has a lot of features. But why I responded is because the fabric itself was the most burly I’d ever seen. 210D Ripstop material like you mentioned in your post and it did feel insanely solid.
I tried it on and the fit was really good. Thin but effective inverted U frame that provided some support but the back of the pack wasn’t rigid. I think it could be good with some running/climbing, even with the hip belt.
It had load lifter straps, hip belt side straps (to cinch pack closer). Big bottle pockets (possibly allowing for two bottles next to each other in each), big stow pocket (not mesh – personally would like stretchy mesh, but this is better for off trail or rock use). Minimal padding but effective. Very comfortable. Two outside top slid pockets (one fleece lined for sunglasses etc.). Nice daisy chains on back of pack.
I’m myself not looking at all for a pack like this but if I was it would be a good contender.
I think you can go lighter, or different form type. If I need this type of volume I like the UD Fastpack 20 mentioned above. This one is more burly, and I think more easy to carry additional weight because of the light frame and hip belt. I just fell in love with the vest design of running packs.
Hope you find what you need.
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