You presume that "attendance" is the valued part of conscientiousness.

No I didn't. That was just one illustrative example. I also included this:

A kid who manages an Art History degree at Harvard while mostly partying and doing the minimal work to pass has a vastly better chance than the a long-term McDonald's employee with a sterling letter of recommendation from his boss.

Getting a sterling letter of recommendation means more than showing up. At McDonald's, praise from a manager would probably be very close proxy for conscientiousness.

I'd consider the college graduate far more qualified - I know they can handle a deadline and open-ended long-term tasks, and even if they appear to be slacking off, I can trust that they have the conscientiousness required to pull through in the end.

Note that you're just assuming that what lets the college kid succeed in passing in the end is conscientiousness. You could just as easily say, "I can trust that they have the intelligence required to pull through in the end." In fact that would be an obviously better fit, since someone who slacked off all semester isn't likely to make up for all the studying in hours that other students did. Instead he or she will rely on intelligence to quickly grasp enough concepts to pass.