I might use the word "accuracy" instead of "correctness," because my thoughts immediately went to political correctness and how challenging it can be to navigate ever-changing norms. But I agree with you completely and have to compliment your willingness to work with new writers. Detailed feedback is always a blessing, even if the comments are hard to take.

But I have to say that I hate Grammarly...particularly its lack of picking up on context and nuance. I'll use it if a client asks me to, but I reject most of the suggestions.

My biggest problem is my vision. It's always blurry by the end of the day, and I have to increase the text to a ridiculous size to catch typos!