Do one video with you doing the intro. You begin by explaining that it's easy to show results by using previous students' performance. You then cycle through all the student  testimonial videos quickly. Video cut back to you teaching viewers that individual, preselected successes don't paint the full picture. The right way to evaluate the merit of a course is to look at the big picture  You show the big data on the right. Video end with a small link in case viewers do want to see the student videos you mentioned earlier.