Steve, you beat to the punch. AFSC's are a 1 way street. I.e. A particular AFSC may require a specific degree major, but a degree major doesn't automatically mean you have a better chance at a particular AFSC. Unless it's mandatory. Like Flieger mentioned, you need a Bachelor's degree to become a pilot. The degree can be in Aero or Art History. And the aero degree will not give you any better chance of getting the pilot slot. A person with a chemical engineering degree might end up with a job in public affairs.
There's a lot of "5 and Dive" academy graduates. They may have gotten a mega science degree for the sole purpose of when they get out of the military. They want to serve, but only for 5 years.
How many aero degree cadets actually get a job/afsc in a field that required an aero degree? Or one where the degree helped them get the afsc??? No idea. But I would definitely think that it's less than half. I don't think there's that many engineering jobs available. But as you can tell, some become pilots. Some get engineering. Some want the degree for later, and take a job in supply, intel, services, etc....