In Australia according to https://taginfo.geofabrik.de/australia-oceania:australia/tags/boundary=protected_area we have 8,586 as relations and 3,802 as ways so both are used and valid.

Until OSM can better support retaining an object history as it changes between a node/way/relation I'd prefer to leave it unless it needs to be changed. Sometimes it's unavoidable so we have to accept the history becomes more fragmented.

It does show in iD though, if you select the way then select the relation that the way is part of you end up with https://www.openstreetmap.org/edit?changeset=165531563#map=17/-33.737030/151.157836 which is the relation selected.

I'm not saying we can't change it to a way, but let's discuss and consult other mappers first.