Device group operations without 'du' service

[ranjith-t]

Hi,
I was under the impression that the device groups are based on tags and tag values in the IoTHub. however, from the documentation it looks like they are tied to 'device update' service. For example a device group delete CLI listed 'az iot du device group delete' is with in the 'du' service.
what is the purpose of 'du' if we are not doing deployment but only operations such as direct methods and twin update?

does this mean that the SDK service will not have a API for device group? Can someone explain how a device group can be created, deleted without device update service?
As per me, by adding tags to list of devices they will form a device group. And when the tags are removed from all the devices, the device group is removed/deleted. For any device group operation, the filter would be the tag/value to simulate a device group. Am I missing something ?

redirected to here from the qn at Azure/azure-iot-sdk-java#1770

My question is more about APIs such as scheduleUpdateTwin() nad scheduleDirectMethod() in scheduled job clients. Isn't these suppose to support device group as well? what is the reasoning for using device update service for these functionalities when there is no update is happening? Isn't this a overhead for the system?

also, if these functionalities are moved to device update SDK? if so, does that mean these APIs are obsolete?