Thanks to all who replied and offered me some input. I greatly appreciate the fact that you took the time to help shed some insight on this matter.
I guess we as parents did not understand the ramifications to applying to an impacted major. Nobody ever brought this to our attention…on the school tours and info sessions when we visited the UCs, at our high school (ie, the guidance counselor), other parents, other students, our child, the college and career office at our high school, reps from the visiting collages, etc. We had been in touch with all these people, many of whom are experts, and never did the discussion of whether to apply to an impacted major ever come up. Furthermore, we did not know to even ask the question. Had we known all this ahead of time, he may have instead wanted to put down a different major other than mechanical engineering. Now it feels like it may be too little/too late.