Law A Level isn't particularly rated for the same reason that A Level 'Medicine' wouldn't be: the discipline is too vast, too far-ranging, to be able to represent on a small-scale. There are far too many different skills involved and far too much knowledge required in order to be able to do so; even if you could somehow create something that was intellectually rigourous and very challenging, it'd still contain lots of learning by rote, AND, even if you could somehow engineer it such that the course tested all the required skills, it wouldn't be in substantial or equal measure.
Admissions tutors and employers would likely much rather see you demonstrate the transferable skills in other, more in-depth, purer subjects. Same with Medicine.