For the sake of discussion..
Just perusing the interwebs but 1000 denier is roughly 11 oz. of fabric per square yard and 500 denier is roughly 5.5 oz. per square yard. Tailoring gear for horses is a completely different animal, pun intended. So to say that 1000d is close enough to 500d in weight per yard is not a correct statement, it's twice the weight.
Remedy 7 - 1000d, 4800ci, 9lbs
Barneys Packs - 500D
Kifaru Packs - 500D DT 6lb 12 oz, Bikini T 4lb 14 oz
Mystery Ranch - 500D, Metcalf 3600-4500ci, 5lb 12oz
Stone Glacier - 500D, Terminus 6300ci (I chose this because there was not a comparable lower CI bag) 4.07#
Kuiu - 500D/160D, 5200cu model, 5lb 9oz
Products are foregoing a minimalist approach and these new packs are almost twice as heavy. 4lb is a lot. So lb for lb, and taking into consideration what is already on the market...what is it that these new packs bring to the table that separates them from everyone else or makes them better?