These limits are designed to facilitate public literacy. This basic difference in purpose makes no difference in scribal training. When we think of scribes, we should think of stenographers, not modern calligraphers. Scribes always have to learn the basics of their craft through an apprenticeship. They have to become so proficient in their skills that writing itself becomes totally automatic, even robotic.
Copying is one of the ways by which apprentice scribes learn.
Professional scribes had more important things to do, such as take dictation. We depend upon ideographs to distinguish scribal hands. Nor should we make the mistake of thinking of scribes as menials. Scribes in antiquity wielded a great deal of power. BTW, when the Greeks took over the Phoenician writing system, they also took over the Semitic size system.