I think we've all seen that video. I think the problems that are revealed there: not enough inertia in aiming/looking around in assault position, and it's too easy to fire while in motion ie not a stable position. He really whips that thing around too fast back and forth as (obviously) easily as flicking your wrist with the mouse and has no problem accurately firing it while still moving.
Another idea is to have the stamina bar affected by just having the MG in assault position, and when stamina bar is depleted you have to rest before you can resume the assault position. This would change the look of the play shown in that video by a lot.
Of course, the Russians in the vid look like they are playing another game, they are terrible, but it doesn't excuse the inertia!
"Sway" itself is not an issue unless you're moving, because the proper tripod position isn't going to produce much "sway".
But the thing is even firing out of an improper position is going to have deadly results at the mostly extremely close engagement ranges shown in the RO2 video above, especially if you have trigger discipline and limit your fire to short bursts.
Even with "moar sway" there will be almost nothing you can do against it in those situations where you are surprised by an MG assault at spitting range and have one bullet to fire before you'll be dead.
He should be able to "assault fire" it with relative accuracy at close ranges, only when not moving, and the aim/mouse control should have quite a bit more noticeable inertia (mouse lag). Recoil control should be insanely bad when walking around...problem is like I said in short bursts this guy is going to get similar results. He probably wouldn't last nearly as long with more inertia though; being able to whip around as if he were holding a plastic toy saved him. Because you can't turn your head in this game, mouse lag for assault MG will bring in one artificial disadvantage (impaired situational awareness), but when the look is tied to where your bullets go, that's the way it has to be.