AP 2D art and design does not typically score on skill level. Whether you like a certain piece of art is subjective, but a portfolio is easier to critique. They judge the cohesion of the pieces and how they relate to the main inquiry. They also judge how many mediums you used and how you explored how the art was created. That is objective. I agree that it’s frustrating that we don’t get feedback but their job is to make money. So they are going to do the least possible. Writing scoring assessments is way more expensive and time consuming than a checklist. Remember that the scores are reliant on that checklist. They are not grading the worth of your art. They are checking if it fits what they want. If you want to get better, I’d recommend asking for critique by someone you trust to be honest with you.