Dual screen was a great feature with a handheld with two tiny screens. They tried it with WiiU on the home console and it was a massive failure. The Switch maybe doesn’t have dual screens, but the single screen is bigger than even the 3ds screens combined and they managed to port almost all WiiU exclusives to it with minimum loss of functionality.
Maybe the revolutionary feature was the added screen real estate the dual screens allowed for instead of there just being two screens.