Honestly, Fallout was never about surviving in a post nuclear wasteland.
It was about role playing in a post nuclear wasteland with some elements of survival in it (your own, characters/factions you encountered).
Wherever did this idea of Fallout Survival Sandbox come from?
But regarding super weapons, a Fallout game plot does not have to revolve about them, they can help shape a plot but do not necessarily be the focus of it.