SERVER-83078 is adding a suite like replica_set_jscore_passthrough but with replica set endpoint enabled, meaning commands like explain will be executed using the router code paths. There are some structural differences between the explain result returned by a mongos and by mongod. There is already a util file (namely analyze_plan.js) with helpers for handling the differences but some of the helpers (e.g. this) currently would only parse the explain result differently if the host returns the hello response with "dbgrid" which doesn't cover the case where the host is a mongod acting as a router when replica set endpoint is enabled since the mongod by design still returns mongod hello response. Also, there are a number of jstests/core tests that don't even use those helpers because they are currently not being run in sharding suites.