When there is an increase in replicated write ops to a secondary, serverStatus includes stats for reader threads waiting for a global lock Global timeAcquiringMicros r, but doesn't report how this would have impacted the thread reading the oplog to replicate to another secondary (in case of a chained replication).
It would be good to have "thread time waiting for a response from replication sync source" since that information is useful for diagnosing problematic lagging nodes.