Since I haven't had free time to knuckle down to AFM tests, I just want to blow a whistle on a couple of general things.
Many ARMA pilots flying AFM forget about the distinction between the weight of an empty helicopter and the weight of the helicopter WITH fuel and essential mission equipment. Usually, the latter limits the payload of most helo types. For example, UH1C took up to 242 US Gal = 920 liters = approx. 745 kg of fuel. So, apparently what you were referring to is "useful load", while you probably should notice that the "payload with full fuel and essential mission equipment" of every version of Huey is significantly lower, thus reducing the allowable number of passengers.
Another thing I like mentioning in the context of AFM is the impact of environmental conditions on engine performance. The typical climate for flying in Vietnam - hot, humid and often high - greatly reduces lifting power. So, as far as "real" realism and historical correctness are concerned, there are written Vietnam war memories of ex-helo crew members about skidding down a runway as often the only method to get airborne on a hot day. And that includes dust off sorties too, which by the way weren't cramped by heavy equipment, right? 😉 It's just something worth realizing and putting into context of that war AND context of the approach Devs have taken to portray such limitations in their product.
It doesn't mean you are not right with other things or you are not right with everything 🙂 As I said, didn't have time to thoroughly test an application of AFM in the SOGPF helos. It's just some misunderstanding of certain concept among AFM pilots I noticed throughout the years of my playing the game 😉
PS. BTW, where did you get the information Hueys were commonly used to transport M151 across the battlefield? I went through tons of Huye's pictures from that era and was able to find only one picture from 1969. For me, it was apparently a test or short shift over an airbase, most likely in HOGE conditions tho.
https://c8.alamy.com/comp/FFGXBW/a-uh-1-transports-a-jeep-over-south-vietnam-in-1969-FFGXBW.jpg