I agree that it’s not as high as the headline number would suggest for the purely unhooked applicants (principally white and Asian students) but I don’t think the number of perfect scoring hooked kids would be so large - that’s why people here and elsewhere feel it is such an uneven playing field because athletes and legacies, overall, get in to with lower stats. As for URMs, this forum gets so excited when a high GPA, 1500 SAT URM asks for a “chance me” (while a high GPA, 1550 SAT white or Asian applicant will get a “meh” and “good luck!”) so I don’t think there will be that many perfect scorer URMs (I would love to be proven wrong on this).
But say you’re right and the admission rate for perfect scoring unhooked applicants drops to 20% (from a headline of 35%), that’s still very good - a 1 in 5 chance is much better than 1 in 20/25.