Concur - COMPLETELY! You think the biggest thing is the gas port - and I agree with that. Now I'm about to go South on you...
I think the biggest thing to START with is a recoil system that will handle the pressure and power of these bigger cartridges. First. If your recoil system isn't gonna handle it, then you compromise everywhere else to make it work... 5.4oz buffer, minimum, if you're going crazy on a load, but optimum at that weight for normal charges, for the Big Frame AR, just to start with... You have to have a spring that's matched to that, too. Hell, the entire system was designed around that principle. Once you've got that - it's all about dwell time and pressure - which is all about gas system length and gas port diameter.
I wish I could work in your shop, brother. Even on a vacation. We could fuk some shiit up.
So many companies these days are literally "cheaping out" and building the cheapest buffers they can (means, tungsten and stainless is expensive, compared to steel and aluminum), so they "under-recoil" these things, and come up with a screwed up spring to "kinda" make it work. Directly downstream of that is making their gas ports right - or not. They often don't. People bitch, and think they need an adjustable gas block to tame down this vicious over-gassed .308 Win AR round... and here we go. It was never over-gassed. It was always "under-recoiled" because it was cheaper to build that way...