Speaking as a parent of an athlete at Princeton and a thespian/musician at Vassar, I think there are a couple things here. First, the sports where the Ivys, including Princeton, are bending standards beyond the general run of the class (assuming we can agree that one standard deviation above and below the mean is the normal distribution for admission) are sports that are all drawing more alumni/general interest than pretty much any other extra curricular on campus. The sports everybody complains about are football, basketball. hockey and maybe lax. In all the years I have been following recruiting, I don’t think I have ever heard of a crew kid, fencer, squash or field hockey player get offered a likely letter with anything other than stats you would assume to be competitive for admission generally. And yes, I am sure there is some example of a true Olympic level talent runner or swimmer getting in with relatively low stats, but that is not only a singular talent but very rare if it happens at all.
Second, I think people generally underestimate how high of an athletic hurdle kids who get likely letters have to clear. Even in football, while the talent generally is nowhere close to P5 level, you are talking about kids whose skills put them in the top couple percent of the million or so kids playing in high school. And those are the normal kids on the team. The kids who are benefiting from real admissions help are generally P5 level players, so well within the top one/two percent of high school players. My guess is that a tenor that the Whiffenpoofs really want with similar level talents is likewise provided consideration by admissions. There is just no quantifiable data on this point. As an example of what I mean, my daughter is a talented thespian, and in my unbiased opinion should have won a Tony for at least one of the three leads she had in high school performances, if not for one of her many featured roles in community theater. But I have no idea how talented she is compared to all of the other theater gerks who applied to Vassar last year. On the other hand, my son had the opportunity to test himself against other athletes vying for spots at Princeton at camps and I can confidently state that while he was fortunate to receive a likely letter as a fourth band kid, if his academics put him in the lowest bands he would not have received one.