I think a better metric is to ask why the documentation isn't better. Nobody is ever happy with their documentation, whether they have too little or too much. But if the engineers think it's because they're being pushed too hard and there's no slack time available to write docs? Red flag. They have explicitly considered the question and realized that the effort to write the docs, compounded by the need to keep them up to date and/or the cost of allowing them to be out of date, is not worth it in their particular situation? Good sign. They feel kind of bad and guilty about the state of the docs? Too normal to be much of a sign, but still positive.