I keep seeing this myth that "you don't even need local currency anymore" repeated.

Multiple experiences in the UK, Netherlands and Italy have proven it to be utter bunk. If you only stay in large hotels and eat in upscale restaurants, maybe it's true. But you are bold enough to try small neighborhood restaurants, shop in locally owned stores, visit street markets and so on, odds are you'll find places that only take cash or nation-specific electronic forms of payment, MasterCard and Visa not accepted.