Hi Max,
I can agree to you on this . In the documentation of the node there is a standard component name given as an example where SAP has implemented an action via dialog.
Also you do have to trigger the action through the method you specified above and inside the action you will only have to write all the logics in the method call type of the action , however you somehow have to control how you are going to share data between the popup and the method call but the standard component BTFSCOA is an excellent example for this .
They have shared data through the global variables of the function module which they have called in there popup to set values and then read those values in the method call of the Action. 
/Hasan