You can absolutely reduce coal and gas without batteries. Hydro is a thing, nuclear also exists. Maybe it's cheaper and more environmentally-friendly to disconnect some solar and some wind from the grid during excess peak production and keep the nuclear running, than having huge storage? Also you're forgetting about the possibility for instant demand response, imagine things like AC units in summer or heaters in winter, where they could be turned on automatically during peak production to keep your house comfier for no cost.