Flags cannot be retracted so itIt might be a case of flagging it first, then attempting to fix it, but not being sure if it's good enough. I don't know.
A NAA should probably be reserved for something that has no value as an answer. Things that can be turned into answers with an edit should be edited.
I really don't see a problem in improving a post after flagging it. Yes, it might mean the earlier flaggers get rejections, but if a little edit turns things around, perhaps they could have done it instead of just trying to delete it.
Flag stats aren't important. Good answers are.
That all said, I'm not sure there's any value in quality of language edits to something that is fundamentally not an answer.