I believe what happens to you and your collegue, you, but it is very anecdotical.
Do you have any classmate that went to all lectures, had a GPA near 5 and scored 98 % in USMLE? I know that case, but it does not prove anything , except that persons are differents.
I assume that you had time, while skipping lectures, to study statistics and scientific methodology...so you know that a good way of demonstrating this subject would be to design an experiment.
First: the objectives:
a) Lectures are not important regardeless of their quality
or
b) lectures at my university were not important?
Take a sample of students, using the same selection criteria, alleatory divide them in two, make one of the groups to attend lectures in an appropriate environment (a or b, depending of what you want to prove), and give the books to study to the other group, that is not going to be allowed to go to lectures.
At the end, we could compare the results and have a conclussion.
(Of course we could make a better design, it is just what I can figure out in this five minutes that I am using to make my point!)