There are two man limitations your ignoring. The arm is less precise so you need longer strokes, and changing pen pressure is much harder. Combined it's far harder to create a legable and fast script.
All fine hand control (fencing, kitchen knife work, writing, eating with chopsticks, soldering, knitting, playing a piano, ...) uses a combination of whole-forearm motion, wrist motion, and finger motion. The human brain/body are incredibly good at translating intended action into precisely choreographed movements combining multiple muscles. The question is how much of each type of motion to use; the more the work can be offloaded to the whole arm, and the more relaxed the wrist and fingers are, the more comfortable it is to do something for a long period of time. The fingers still do quite a bit of fine motion, regardless.
But my comment doesn’t even advocate any particular grip or hand movement technique; all I said is that those bits of advice from the Palmer school, under discussion by the top-of-thread poster, are applicable across various letter-shape styles. As far as I can tell that’s a completely uncontroversial statement.
There is a wide range of comfortable shapes people can make using whole hand motions, but arms have a vastly more momentum than the tip of a pen. So for example the center of an uppercase E is much harder to do using whole hand motions if you need to stop your arm motion in the middle to add details. It can be a fairly direct tradeoff between legibility and readability. Scripts that are less legible because they lack detail can quite simply be far easier to pull off.
All fine hand control (fencing, kitchen knife work, writing, eating with chopsticks, soldering, knitting, playing a piano, ...) uses a combination of whole-forearm motion, wrist motion, and finger motion. The human brain/body are incredibly good at translating intended action into precisely choreographed movements combining multiple muscles. The question is how much of each type of motion to use; the more the work can be offloaded to the whole arm, and the more relaxed the wrist and fingers are, the more comfortable it is to do something for a long period of time. The fingers still do quite a bit of fine motion, regardless.
But my comment doesn’t even advocate any particular grip or hand movement technique; all I said is that those bits of advice from the Palmer school, under discussion by the top-of-thread poster, are applicable across various letter-shape styles. As far as I can tell that’s a completely uncontroversial statement.