It got better exchange rates than cash machines and visa on a recent Italy trip.
Because the card issuer of your Visa would have loaded the exchange rate for both purchases and card purchases.
Visa/Mastercard have an excellent exchange rate, better than any other rate a tourist will get. Some card issuers will then load it themselves, so avoid those, but the fact remains, the stock Visa/Mastercard rate is superior to the rate Amex will offer irrespective of the country you are in. There are cards which do not tamper with the rate Mastercard/Visa offer.
It's a matter of pence versus the very best anyway and I prefer the airmiles over the faff of another card for a slightly lower exchange rate.
I'm sure you do prefer the airmiles but the bonus's you refer to are unachievable for most people. You mentioned the Companion Voucher. You must spend £20,000 in one billing year to get that. You like the airmiles, Amex like the fact you like the airmiles too because for normal spend you earn 1 Avios for every £1 you spend.
15,000 Avios gets you a return flight to Rome - though you still have to pay the fees. So if you wanted 2 of you to got to Rome with your airmiles make sure you spend £20,000 on your Amex in one year
It only works if you can rack up loads of Avios through promotional new-card offers, or by putting huge amounts of business spend on it, etc etc. For day to day average person use its just pointless and those benefits you crave meaningless.