The fact that there weren't any service edits returned is a little suspicious (check your server logs for any message, and you can increase the logging level temporarily if you really want to dig in). I was able to verify that this worked on my end using the following parameters, looking directly at the subnetwork table without coded values helped me make sure i put everything in correctly.
Afterwards i was able to confirm that the subnetwork controller was marked as deleted. If you had your ArcGIS Pro session open when you ran the command you may need to refresh your view of default to look at the latest edit moment by selecting the version in your list by data source tab and selecting refresh on the version tab.
Once I did that i was able to see my subnetwork controller marked as deleted. From here I would follow the rest of the process for purging the subnetwork from my system (update subnetwork, export subnetwork w/ack).