Mystery ranch’s futura harness system is quite good, especially anything with additional structure like the guidelight frame or CF/aluminium stays. I have hiked with 55 pounds in one of their ~1500 cubic inch backpacks with the most basic futura yoke system and 1 inch waist belt and it was fine. Looking at their catalogue, the scepter 50 is 3 pounds, the X-55 is 4 pounds (X-pac) and their terraframe tri-zip 50 is 4.4 pounds.
Hill people gear i think are superior to mystery ranch in their hipbelts and compression systems. I have not run heavier weights in them, but given these advantages i think it should be superior. The modularity of their system is also nice, but overall they seem heavier than some mystery ranches lightweight options.
i would like to try some hunting frame systems like Exo, kuiu and kifaru. Seek outside looks good too! Technical load bearing is a fascinating subject. Carrying lightweights is not a problem; carrying heavy weights is.