Power plants right now have to optimize for working around varying wind/solar supply, but if we tried to run civilization on wind/solar alone, we'd rediscover the need for good baseload supply when the wind stops blowing at night.

Actually no, because this function is already being taken over by gas peaker plants. It's less expensive to have such a plant and fire it once in a while than to keep a large nuclear/coal plant churning.

Both of us were talking about the long run, and what I said was "wind/solar alone." Of course we can run on wind/solar/gas but that doesn't decarbonize the grid.