I have been an aspiring writer of sorts, and wrote articles at least once a week for several years without getting much if any feedback on the quality of my writing as opposed to its content. It is fairly easy for me to look back and see a steady improvement in writing quality. I also usually (not always) have no trouble knowing which of my writing isn't any good, and don't remember it having been otherwise.

I could be deluding myself but I certainly think some of my writing is better and some of it is worse.

Well, I'm not an aspiring writer but as an amateur musician and visual artist I can say that I can generally tell when my works are not as good as I would like them to be, and I can generally guess ahead of time which pieces will have a better reception among my more critical friends.

In addition; I know a couple of aspiring writers and if anything I would say that they are often very self critical and judging by what they have openly shown me against what they have reluctantly shown me I would say that they did indeed have a good sense of what was good and what wasn't.

Based on my experiences, I would say that it is fairly common for artists to have a fairly accurate awareness of their own shortcomings; whether or not they can successfully ascertain a workable procedure for overcoming them is a different issue.