If 30% of the student body requires remediation, then that means 70% does not, and I don't see how the 30% affects the 70% in any way. If Harvard only accepts a certain number of TJ students, then obviously they'll be picking from the top 70%.

I went to a public high school in a blue-collar exurb. Any macro-level study of the school would suggest that its primary contribution to the community came on the football field, as test scores were atrocious, truancy was high, ESL was in high demand, etc. But the school also had a robust AP program, a commitment to excellence in the arts, etc. The end result was that while probably more than 60% of my school required remediation in some way, those students and their needs had no impact on the quality of education available to me.