The problem is not the "hold" most people on this site are talking about AR10 rifles and using a bipod with a rear bag or other support. Not shooting from an unsupported position.
Just as noted by @
calimwulf, who is a perfect example, people may know the phrase,
fundamentals of marksmanship, that doesn't mean they know what they are or how to properly execute them. The fundamentals are, Sight Picture, Breathing Natural Point of Aim, Trigger Control and Follow Through and are not to be confused with the elements of a good position. Those are different, most repeat some of the Seven Factors and 3 Elements which support the fundamentals, and often confuse the group creating a hybrid understanding. These factors can vary slightly from system to system as well as position to position, but they are all designed to support the proper application of the fundamentals of marksmanship.
As far as the Mk11 shooting flames out of the ejection port, I have seen this and most of the shooters are still able to maintain at least 1 MOA of accuracy out of them. Not great but not awful. This is where the other side of the bolt comes into the play the Buffer Spring. This part in the rifle determines the amount of time the bolt stays locked and how much gas will begin to move the bolt. David Tubb sells his flat wire heavy springs specifically to help function but to also assist in accuracy. How does the buffer spring affect accuracy if the system is moving after the bullet leaves, well it doesn't always. It control the hold on the bolt carrier group. Many stock springs are too weak and not correct so they allow the bolt carrier to begin moving, its not always over gassed, it's under sprung... by moving to a Tubb Flatwire spring you keep the system locked up longer. (
that whole we can move just as fast thing) Hence more accuracy, like decreasing lock time so we can't beat it by replacing the trigger. Much of the inaccuracy of the Army rifles came from the suppressor, it is a 2 point system that attached at the end of the barrel and back at the gas block. By heating and cooling at different speeds of different metals, you affected the harmonics. Remove the suppressor you saw accuracy increase. There is a lot that goes into these systems, and no one thing is a magic fix, the shooter was just as much part of it.
I said before, AR15s and AR10s are apples and oranges. You often hear guys who think they are good with an AR15 argue against the quirks of an AR10, but they are there, its much more mass, a big, SLOWER bullet, and a lot more gas that move very fast. Having a weak buffer and that bolt carrier is moving and video an M4 is not showing the differences.
AR rifles in general are a giant tuning fork, how you address it, and the trigger matters. Even when shooting from a bipod, that movement at the trigger matters. Remember in a bolt action rifle, adding a canted base is about 1 thousandths of an inch at the receiver per 1 inch of movement at 100 yards. If we move any part of 1 thousandths of an inch at the trigger, or at the stock, we are adding that x100 at 100 yards. 20MOA bases aren't inches apart from a flat base, but about 15 thousandths of an inch different. We can certainly move fractions of that, and much more quickly then you might imagine.