Please confirm that MedicationUsage should not include redundant information found in MedicationRequest, MedicationAdministration, and MedicationDispense? There seems to be no direct link to any of the mentioned Medication[x] resources that existed in the R4 MedicationStatement. This should be explicitly described under the corresponding section(s). 

Verbatim 11.4.2:
"The MedicationUsage resource is used to record a medications or substances that the patient reports as being taken, not taking, have taken in the past or may take in the future. It can also be used to record medication use that is derived from other records such as a MedicationRequest. The statement is not used to request or order a medication, supply or device. When requesting medication, supplies or devices when there is a patient focus or instructions regarding their use, a MedicationRequest, SupplyRequest or DeviceRequest should be used instead."