There were joysticks with buttons way before the NES. Do you consider putting a piece of plastic instead of a joystick a major invention?
I think the fact that there were many joysticks before the NES came out, and many other kinds of input devices, kind of shows that the d-pad was a non-obvious invention. In hindsight, it seems super obvious, but back then, it was a major invention.
And the Atari 7800 controller from 1984 does not qualify as a gamepad? Come on...