My engineering class started with about 140 and graduated 38. Most of the weed-outs happened in Freshman Physics and Calc.
Kudos to your son for testing out of the easy stuff. I did the same (12? I think? English credits....).....left time for me to work on the important things.
He's worked hard, and has pieced together enough scholarships to earn a ride. It's tough on him, because their renewals are dependent on grades. It was all A's except 1 B the first semester, but all B's except one A the second.
One thing is for sure: He's now grateful that I insisted he take the most demanding courses he could in high school, including the dual enrollments.
To paraphrase my boy, "It's hard, but at least I'm not trying to do it while writing a paper on Hamlet."
For the life of me, I don't understand why more of the "academic elite" students don't take more dual enrollment courses in high school. He might have made a 93 instead of a 99 for his senior English, but the payoff has been tremendous.