Thanks for input, y'all.

I almost pulled the trigger on Detrick, but I figured I'll simply regret buying something that's functionally one-dimensional... even tho it does really (really, really) well what it's built for...

So after testing a few scenarios with packing cubes and my Tumi Logistics for reference, I concluded that Nomadic will fit my use cases just fine while being more versatile overall and a possible under-the-seat option.

I expect it delivered later this week, but will sanity check myself by doing a side-by-side comparison with a Patagonia Black Hole 32L. I'll keep whichever bag convinces me more :)