They haven't done anything wrong and should not be criticised. They always had a term which said if you didn't keep your policy for six months they could take back your bonus points. No one can complain that they are seeking to do this. It was extremely clear that this could happen.
Keep your policy for six months and there wont be a problem.
Four months paid.
I knew the moment I took out the policy that I would be cancelling all of my AMEX cards before the end of the six month period.
It certainly was. I guess some people may have thought that they wouldn't bother.
Don't think this has been enforced in Australia, but I heard overseas Amex do chase former cardholders aggressively if they closed the account and subsequently the balance goes negative (such as points clawback or reversed charges). Have you considered that to be a risk in Australia or the laws here are different? There are plenty of people on reddit who can tell you their experience of having to buy points at 2.5c USD each to cover the shortfall and it's not fun.