ACT Prep courses?

I took the Princeton Review ACT preparation course. Started at a 29 on my first practice test, ended up getting a 30 on my first actual test. I continued to study with the Princeton Review course and improved to a 31 last December. I took a break for 6 months and did not study at all. My friends all studied a ton and worked so hard. They got 30-32. I didn’t study and magically got a 33, with a 34 on science (I usually get 27-29). Does this prove that ACT preps aren’t helpful (or aren’t worth the $800)?

With prep course: 28 on science, 30 and 31 composite
No studying, No worries: 34 on science, 33 composite

Well you still had the prep course.