Harvard’s CDS mentions 58% of first time freshman received need based FA from the school. The 70% figure includes other types of aid. Harvard gives need based FA for some families making $200k+, so the % of students receiving FA is not a good metric for measuring the portion of lower income students. Instead I’d look at the income stats in the freshman survey. It looks like the median self reported family income was ~$150k, with 35% coming from wealthy families making $250k+ and 13% coming from lower income families making $40k or less. So while there are some lower income students, a larger portion of the student body is wealthy than at typical colleges in the United States. A similar pattern occurs at most highly selective private colleges, although generally not as extreme.
I attended this type of selective college, while having a family income that was far below the median. Personally, I didn’t even think about how my family income compared to others. Students I knew didn’t intentionally flaunt their wealth or only associate with certain income level students. Instead I had no idea how much the family’s of the vast majority of students made, nor did I care. Similarly I doubt family income is a big issue for most students at Brown. This is quite different from typical US high schools for a variety of reasons, including having more direct family connections while in HS (for example visiting friend’s much nicer house, parents having to explain that they can’t afford spending $4k for cheerleading like friend X’s family did, etc); so I can see why HS students are likely to have different feelings.