As I understand ballistics, you are pretty much spot-on, Rich. I am not a ballistician either. For ANY given projectile, the slower it is traveling, the faster must be it's RPM to maintain stability/stabilization.
That is why muzzleloading pistols, to be accurate, must have quite fast rates of twist. The slower moving projectile needs a faster rate of RPM. A slower rate of twist in a pistol, requires a LOT more powder to get the velocity up to where the ball is stabilized. We know that slower rifling twists, require more powder to get the same accuracy that a faster rate of twist can produce.
It takes more power to get the rate of spin up, ie: revolutions per minute.
Round balls require little spin (compared to conicals) to stabilize, yet, they still must be spun so that do not take on an atmospheric induced spin and curve off course (line of sight) due to that spin
as in a curve ball in baseball or the way a side spinning golf ball curves or hooks. They must also be spun fast enough, to stabilize at the range required, whether this is 100yards, or 300yards.
That is why those bench rest rifles that weigh 50 pounds in .69 calibre, use 200 to 300gr. of powder for shooting 200yards.
As we progress into conical projectiles, the longer the projectile, the faster it must be spinning to maintain stability/stabilization. This requisite rate of spin for any projectile can be effected by increasing the velocity, or increasing the rate of twist in the rifling.
The longer the range we are shooting, the slower the projectile will be traveling at distance and since the slower moving projectile needs more RPM for stability, we must drive it faster to start with.
The slower the rate of twist, the faster we must drive the ball to stabilize it for the given distance needed.
For example, my .69 will shoot the same size groups at 50yards, using 85gr. of 2F powder, as it does with 140gr. 2F powder, yet that 85gr. powder does not shoot well at all, at 100 yards or further.
For that distance and further, the rifle needs at least 140gr. 2F powder. Back when the rifle was new, it needed 165gr. of that 1986 powder to shoot well. Today's (2000's)GOEX powder is slightly better than the 1980's GOEX and that is the difference, I assume.