Thanks for getting back so promptly.
You are correct in saying that the osm data model requires to pick single wharf for each end of a route.  For TfNSW to use the osm ferry network for routing led to 2 options, 1) map each variant as route or try to simplify the network by still trying to maintain the main routes. which would just be a big spaghetti mess 2) but rather add segments in between to connect various variations.

We did approach the osm-au community which has a bit more detail about our approach - https://lists.openstreetmap.org/pipermail/talk-au/2018-August/012012.html

We are happy to simplify the network and clean up the relations but hopefully you understand our view and we as TfNSW can keep using the osm ferry route network how we have in the past.  

at the moment Sydney Ferries 61 variants out of 206 are non routeable
and 25 out of 72 variants for Private Ferries. I just sent you a message with link to kmls that gives more insight.