So for example, by this standard the biggest cost of college for many people will be not tuition, but the time they spent in college that could've been spent working.

Not disagreeing with anything in the post, and I acknowledge that this logic makes sense if you're primarily measuring things in money, but I'd just like to note that this example is likely to come off as weird to the kind of people who like to study but who are unsure of whether there's any job that they'd enjoy. For them, having a socially-sanctioned opportunity to spend several years not working isn't a cost, it's the whole point of going to college.