Bhavnani and Lee have a counterintuitive insight.
the performance of bureaucrats hired through affirmative action is similar to those who were not, is striking within the context of the polemical debate on affirmative action, in which strong claims are often made for the positive or negative effects of affirmative action. We find that reservations have neither led to hiring of officers unable to perform their jobs or led to a dramatic change in institutional output, at least for one important government program.
They use the provisioning of MGNREGA at the district level as a proxy for bureaucratic performance. Their major finding is that MGNREGA provisioning does not worsen in districts where the IAS officer is a beneficiary of reservation.
Two possibilities arise if this result is reflective of the reality. One, UPSC exam performance does not reflect aptitude for governance. Or two, getting into the IAS is so competitive that despite reservations, efficiency of those with lower ranks is not compromised.