PBA – the grading method is determined by the professor. Most professors I’ve had were explicit in their requirement of proper writing format. Even those who weren’t explicit generally gave the best grades to the best writers.
Granted, I’m providing personal experiences.
What evidence do you have that “most” law schools have an A+? Or that writing ability is generally the “least” factor? At best, we had different experiences. Are you the chronicler of all law professor/school grading procedures?