However you frame the question, "these 8 universities" or "the 8 universities which produced the MOST centimillionaires", neither "lower than 35%" nor "I’m a little surprised it’s only 35%" is an actual numerical percentage. This is not a percentage either: "you should expect the subset to be over represented compared to the group."
However you want to frame the question, what were your priors, and why? You haven't said what exactly you would have guessed. I had no priors for either framing of the question.
Stepping back, the point is that putting the disparity of wealth into numerical terms is important because otherwise we generally have no measure of wealth disparity, just a vague recognition that some people are wealthier than others. It's unclear why you or I or anyone would have prior % estimates, based on no empirical studies, only vague impressions of society. There's a point to studying things empirically and comprehensively, which is to teach us things we didn't know before. I'm skeptical of any claims that "This is nothing new or surprising", as if laymen magically had intuitive access to these empirical facts.
Also, what's notable about those 8 universities is not just that they produced the most centi-millionaires but also that they're very difficult to get into and obscenely expensive. Access is extremely limited. And of course they have "legacy" admissions. We know that wealthy and well-connected people go there, and we know that ambitious kids want to go there (as evidenced by their very low acceptance rates).