Not all great philosophers are great at math. As my senior thesis advisor at a high-ranked Ivy told me: "Some of my colleagues here aren't good at math. It doesn't really matter unless you're going into philosophy of physics, etc." And then there's the notable example of Derek Parfit. From a New Yorker piece:
In the autumn of 1961, [Parfit] went up to Oxford to read history. (He studied Modern History at Eton, which for England began when the Romans left, in 410.) He was a little bored by the subject, and briefly considered switching to P.P.E.—Philosophy, Politics and Economics. He was apprehensive about the mathematics that economics would involve, however, so he read a few pages of a textbook and came across a symbol he didn’t recognize—a line with a dot above and a dot below. He asked someone to explain it, and when he was told that it was a division sign he felt so humiliated that he decided to stick with history. After Oxford, he went back to America for two years on a Harkness Fellowship. ... He decided to study philosophy.
I hope that adcoms keep this in mind when they're faced with that final list of 20 students and are looking for reasons to cut someone. But who knows these days.