As seen in BF-30845, there is a change in $queryStats performance related to SERVER-79736. This is only for the case when $queryStats is invoked concurrently with find commands with no rate limit. We spent some time looking into this and ruled out some theories, but ultimately did not get to the bottom of it. If the rate limit is ever turned off and/or if we would want to run $queryStats more often, it would be good to know the root cause for the regression.