I have had two disputes with Amex, both in my favour.
One, an online merchant to charged me a restocking fee for a product he billed me on order, delayed it for a month and then "lost" the product. It was about $25 and was done without any argument.
The second one is when Canadian carrier Jetsgo went bankrupt. Visa/MC dictated that you had to wait until after your flight before you could make a claim, I called Amex, sent in a form, had the charges reversed in less than a week.
No if/ands/buts