I have a strong preference for the Maruspial, but have not tried the muley freak harness, so it isn't for performance reasons. I've always thought the muley freak harness was a "me too" product when it launched to slightly alter the original Kuiu approach, so haven't paid much attention to what that system looks like today honestly. AGC/FHF/Marsupial are all "maunfacturers" and not "influencers" so I don't look much past their systems, as they are product focused. That's all pure opinion.
If I was carrying a weapon on my chest rig, I would want a really good actual harness (ie back part) to support that. I would tend to agree with others that separating the systems is probably a good way to get there more comforably.
Other option is look at that Kifaru steelhead, that's got a built-in weapons carry pouch in the back. Depends on your handgun though.