OP - allow me to say this:
Wwhile I understand your frustration with AMEX, and what you have said may help others, the reality remains simple - Your AMEX's dispute has been finalized. If you want to go after AMEX for this, you will have to file a request for arbitration. This is not the best solution.
Instead - I will simply go after whoever charged you the extra in a Small Claims court.
What matters is getting your money back.