They are, no doubt. I'm not sure whose job it is to make the scoring ruberic, yours or the professor's, but I've found that the more detailed the ruberic, the less subjective grading becomes.
it's pretty hard for it not to be subjective when you're grading 60 essays...skill at writing and a host of other things work for and against you, and that's before working out whether the student touches on everything that you want them to touch on.
and that's before you talk about two papers that might be objectively the same, but happen to be read at different stages in the grading...say, read 10th as opposed to 50th when you're worn out, or doing it on a different day in a different mood.
i only figured this out in graduate school with regard to my own work where i'd notice variance in grades on minor assignments that were somewhat formulaic in the write-up...basically, i couldn't tell you anything different about what i'd produced, but the prof would grade them vastly different. one prof loves your writing, another dislikes it -- this is my favorite aspect of this.
so, note to all you college kids...if you think the grading is BS...it largely is. they've actually done studies proving it so.