What good feedback comments on, in order.
There's a difference between feedback that improves a document and feedback that improves a writer.
Critical thinking and task alignment
The first thing the feedback looks at is whether the thinking is doing any work, and whether the draft answers the task that was set. It works on the thinking, not the sentence.
This is the part a student carries into the next assignment, and the part that changes a grade.
Argument, and whether claims are supported
Whether a claim is supported by the source cited, or merely adjacent to it. Whether the evidence establishes what the sentence says it establishes. How sources have been used.
Structure
Whether the introduction sets up what the essay does. Whether each paragraph earns its place. Whether the conclusion concludes anything.
This is what markers write in the margins, and it's the part students most often never get, because writing it takes time nobody has at scale.
Grammar, spelling and word choice, which come last
Spelling, punctuation, grammar, word choice, readability scores. Useful, entirely automatable, and available in a dozen products including the one already inside your word processor.
It is the last thing the feedback comments on.
Why suggesting beats correcting
Both kinds of feedback can be delivered two ways: as a fix, or as a prompt. A fix is faster and produces a better document this week. A prompt is slower and produces a student who can do it themselves next time.
Studiosity gives the prompt.