Well written, Anonymous. On this much we agree: A college diploma is neither necessary nor sufficient to obtain useful skills. However, I think you overstate your case. College does not guarantee that you will become a problem solver, but if becoming a problem solver is your goal then college can be an effective method of achieving it.
Self-motivation and self-study are important, but not sufficient. In a functional college environment, you will be serendipitously exposed to ideas that you would not otherwise encounter, and would not know that you need to dig into. If you are motivated and want to learn, college is a great place to do that.
On the other hand, my thesis presumes a "functional" college environment. If you want to argue that many colleges these days are dysfunctional, I won't contradict you. It is entirely possible to get a college degree, even an advanced degree, and not learn anything useful. But just because it is possible to waste years and countless thousands of dollars on worthless degree programs does not mean that all college is worthless. You will get out of college in proportion to what you put in. I think even soft subjects, properly done, have value, though I agree with you that the soft subjects are not often properly done nowadays.
Society seems to have conflated the concepts of "credentials" and "capabilities" and assumes that having the first bestows the second. You cannot deny that the two are at least correlated, but the correlation is imperfect and even if it were perfect it would not imply causality. It would be good if more people, and especially policy makers, recognized this.