I see your point, and can sympathise. Nevertheless, let's dig further and see if we can get to some fundamental principle:
> is he/she just comparing based on what “looks good” to the eye.
How are art subjects in school graded? I actually don't know.
> Some people might not have very steady hands. Are you going to penalize them for that?
Some are bad at something else, like mathematics. Are we to penalise them for that? Yes, those students get a low grade in mathematics. Can we motivate a difference in attitude between handwriting and mathematics by an appeal to usefulness, saying that it is useful to be good at mathematics, but not as useful to shape beautiful letters? Is it nevertheless a point in teaching it (and arts)? Is the teaching of those subjects motivated by other things than their usefulness? Should they, because of that, be graded differently, perhaps in such a way that effort, along with performance, can yield a high grade? (What happens then if someone relies on a grade to see how well someone else does music?)