Having a slow impediment to the bullet caused by a slight gain twist is just as important today as back 'then'.
Some modern BR shooters have LONG BLANKS scoped and measured by computers to determine where to cut off the barrel to form not only the muzzle, but the breech as well. When dealing with really high velocities (over 3,000fps) even minor slowing of the twist has a deleterious effect on accuracy - oh, they'll shoot, but they'll never be consistent winners. If they can cut the barrel as the twist rate increases, even slightly, the barrel will be more accurate - possibly a new SCREAMER barrel, possibly not ,but it has the potential to be a screamer - a barrel that shoots in the 1's (for a top shooter), no matter what the wind is doing.
Likewise, this gain or increasing twist at the muzzle must also have a positive effect in our muzzleloading rifle barrels with round balls, perhaps requiring even more 'gain' to make much of a difference, but the physics and science is there - for us.
Hanshi - spot on, imho.