Honestly, this is the biggest thing that I don’t think people realize. I’m a top 5 pre-doc & can think of people without 4.0 or with Q168/169 (not 170) who got into Chicago (this time) /Harvard (last time).
IMO, predoc is the single best thing to do to increase likelihood of admission. Of course, selection into top 5 RA is severe, but even conditional on the selection, the extra two years to develop research ideas and write a strong personal statement, get strong letters, publish/coathur in NBER. Very few people (certainly not me) we able to do that as seniors in undergrad.