This is patently false. If you turn off your WiFi, 4G, Bluetooth and NFC, and only use your phone for calls and SMS, a smartphone can easily last a week. More than a dumbphone with the same features.
Agreed. You can also lower the brightness of the screen when you don't need it. My Sony Xperia Z5 Compact in "Stamina Mode" (basically what you're describing) can last for 7-8 days as far as I can tell.
