I agree. I worked for years at a university, mostly working closely with freshmen and sophomores. I learned from those experiences that it is more common than may be assumed for 18 year olds to not be ready for college life in terms of maturity regardless of educational background. The vast majority of the students I saw struggling had public and private school backgrounds. I personally don't believe that those who flounder (or their parents) are to blame, because things are set up so that we are led to believe that they should be ready and will be ready by 18 when that just isn't the case for so many.
As for your own disappointment, try to focus on what can be done now. Has he reframed goals to fit what is going on now? Once he can do that, he can work to figure out a path forward. Try to think mostly about his strengths. Focus on the now and the future, not on decisions made in the past.