Self-study typically means no graded writing exercises- which for things like US History are really the crux of the AP curriculum.
If you self-study and get a 5-- that’s validation that your skill level is more or less on par with other students who also got a 5 (you probably didn’t work as hard as they did, but you covered the material). If you self-study and get a 2- then yes, you’ve wasted the time you could have spent developing your skills- analytical, writing, etc. taking an actual course with an instructor, whether online or in person.