SERVER-57221 highlighted performance problems on deletes for collections with more than one secondary index and SERVER-57307 mitigates the problem with the use of a hint for chunk documents deletion.
However, the ~17x performance gain showed in
SERVER-57221 does not seem to correspond to the ~5x gain obtained when locally testing SERVER-57307 changes.
Investigate what leads to such a difference. Some options to check would be: interference on the machine, documents size, presence of specific config server hooks/observers, number of secondaries, sharding-specific overhead (since the test was done on a plain RS).