How up-to-date are you on industrial battery installations? I ask because we're literally in the midst of an energy storage revolution, with battery capacity exploding massively in the last 2-3 years and no slowdown on the horizon. You may be arguing from a point of completely outdated information.
And in those extreme circumstances batteries reduce the gas capacity needed, by letting them run efficiently and the batteries handle the peaks just like a hybrid car. They also let you maximise transmission line usage for imports from nearby countries.
The reason why we have been using fossil gas as peakers for decades are because they are about the cheapest we can build while offering acceptable running costs.
We also have an entire fleet of them, which lives are easily extended as long as we add for example capacity markets to ensure their survival as renewables push down their capacity factors.
If you have enough battery manufacturing capacity to make all your vehicles electric, you have enough battery manufacturing capacity to cover a week or two of not just dunkelflaute but even "why is the moon hovering directly between us and the sun, isn't it supposed to be moving?", which is darker than that.