Seems impossible to design one pack that fits a wide range of people really well. If you want a pack that works well for you, you need to try a lot (and return or resell a lot), or get a custom pack.
Now I understand why some packs get rave reviews, but I hate them when I try them.
"I'm curious: if someone were to produce an external frame pack that weighed two pounds or less, would members of this forum consider it?"
Ten years ago I tried the LuxuryLite StackPack (just over 2 pounds), and it was agony for me, even after many adjustments and part rearrangements. Must fit some other people OK because he still sells them.
"Oh wait, even more: how many members of this forum have even used an external frame pack?"
You mean Kelty, North Face, Trailwise, LuxuryLite, and some no-name canvas-and-aluminum pack my mom bought me for Boy Scouts?
Most comfortable pack I ever used, regardless of construction, was an Alpenlite internal frame pack from the early 1980s.
Though my new HMG Windrider 2400 is pretty good fit, too. Got lucky on that one.