> By over provisioning (and net interconnectivity) we can reduce the need for adjustable sources. Essentially if you have enough renewable sources to cover the high demands at low wind/sun you can always turn off the sources when you overshoot and because they are cheap it is economical unfeasible.

Overprovisioning by how much? Currently ( at least since a month or so) across Europe there's a meteorological phenomenon that makes for cold temperatures, lower than usual wind speeds, and clouds. 2 out of the 3 main renewable power sources ( solar, wind, tidal) are heavily impacted ( wind most of all iirc) and producing less electricity than usual, while people need to warm themselves. And this is expected to continue into the winter.

To combat such a scenario if everyone was on renewables+storage+interconnects, you'd have to built massive storage ( which we don't have the tech/space for) or massive interconnects from really far away places like Africa.