Hmmmm, yes, probably. However the reasons for deploying millions of lithium batteries instead of a few dozen pumped hydro stations are likely more political and

Hmmmm, yes, probably. However the reasons for deploying millions of lithium batteries instead of a few dozen pumped hydro stations are likely more political and business reasons than technical reasons. First, it's way easier and faster to just park containers full of batteries wherever you need to shift the energy than to find and build new pumped hydro location then build/upgrade the transmission to the locations where the load shifting is needed. And when you need the load shifting ASAP, you're probably going to opt for the solution that can deployed now, especially when the regulatory reaction to this problem is to adjust prices ("time of use" rates) to discourage people from using power during the slope. Second, battery installers are able to sell directly to consumers, which means they can bypass utility bureaucracy. Many utilities are very slow to adopt "non-wires alternatives" because their business model doesn't incentivize them to building out a distributed, flexible grid, and they are increasingly becoming worried about their generation assets being financially stranded. This means that it's often easier to sell thousands of energy storage units to thousands of homes and businesses, than it is to sell that same thousand units directly to the utility. With pumped hydro, there's no distributed option, so you end up being at the mercy of the utility wanting your product. So yes, you're probably right that pumped hydro is on paper cheaper for addressing the Duck Curve "neck" problem, but this is a case where the difference between theory and reality is substantial for non-technical reasons.