Haha, you are right in that a lot of guys, like your son, stack aid to get a full but there are also a lot of guys on true full rides running XC.
I am a coach on a fully funded, well rounded track team. Three quarters of our aid is tied up in 9/14, men/women athletes. A lot on full rides. Big points expected. But, the vast majority of the team is walk on, with some of books to 10%. Not every team does it this way but a lot of teams do.
In competitive conferences you only need 6-10 guys scoring an average 8-12 points to be top third consistently. Better to have big sccholarships in a few guys.
For OP, take the money.