Many retailers don't take Amex because they charge higher fees, not because they are consumer friendly (which they are).

In my experience, Amex is more likely to respond to a merchant presenting evidence that a chargeback is unwarranted. Visa/Mastercard essentially just say "tough luck," except in the case that a consumer has charged back by mistake.

I work at a bank and have extensive experience with this. Visa and Mastercard protect merchants while American Express protects consumers. Neither are absolute of course but these are the biases that each one has.