You're right that it isn't the full usage of what I could potentially achieve. And right to point out. Alas I'm travelling with a lap infant and a 3 year old, so that means there is a balance between some nice holidays between work, and what I can get away with with the young kids. In this case the Hobart trip will be over the Christmas holidays so it will be good value even if its a short segment... I'd prefer to go back via Perth, but I'm also a bit short of time to make that worthwhile
I had looked at the rules and didn't find anything that justified the agent, so hence double checking experiences. This is only my 4th RTW so I'm still experimenting , the first one had a HKG-SFO-JFK-AUS-LHR backtrack to get a few more US segments in, and fair to say the pleasure of the transcontinental was outweighed by the pain of the JFK-AUS flight which was delayed by 6 hours

Oh and I've got the full rules via expert flyer too.