This approach is notable for benefitting from swelling headcount increases i.e. if you hire 1000 new people, even if only a small fraction will vouch for you,

This approach is notable for benefitting from swelling headcount increases i.e. if you hire 1000 new people, even if only a small fraction will vouch for you, on average you -and everyone else- will benefit by seeing the # of people who listed you in the "top 5 who helped you being productive" increase The old Google performance review was arguably similar (the managers could still punish their reports, but peer feedback was valued a lot more), but I think that Google swelled in size because of other effects (probably because managers might've been indirectly rewarded by having more reports, despite managers rarely being among the people who others would list as "making you more productive")