So summarising,
You cant use it as a Home Control button on your Harmony Hub, is that right?
That was the example I gave, yes. But most other integrations, like SmartThings, require an Entity, SmartThings happens to be the exception in that it accepts scripts as though they are entities, but even that does not interact directly with the Service Command, just with the thing you created to interact with it.
I imagine those integrations from other software not being able to interact directly with a service call is because it’s a legit security concern. Regardless those & others generally require an entity to be able to interact with it