If I understand correctly, settings.getLastErrorDefaults and settings.getLastErrorModes don't really have anything to do with getLastError, but rather are writeConcern-related configuration options. This means they are now misnamed, and should probably be called something like "writeConcernDefaults" and "writeConcernModes". We should rename them or provide aliases.

Note that the getLastError command was deprecated in version 5.0, and the Query Execution team is planning to remove it soon. Therefore, these misnamed options will become even more obviously misnamed, since getLastError will cease to exist in the rest of the code base.