Excellent point...
Isolating the point of movement...also limits the movements...so don't expect to any flourishing. Repeatability...for many, like myself, rehabitation is difficult. So isolation for repeatability. Hence, in leur of consistent results..
Elevation...not everyone will wear a long sleeve and jacket when we write as it is instructed in the manuals. Elevation helped my sweaty muscle pads from sticking on the table, and elevates the entire forearm so that my lazy hands will find some closure to a more formal writing position as instructed in the manuals...ie gliding with only the fouth and fifth finger nails.
This formal writing position is adopted for both broad edge and pointed pens.
For the gifted and most talented, this is not necessary.