The grid storage that has actually been deployed like hydroelectric and battery storage does have cost history. But it's too expensive, and are geographically limited in the case of the former. The grid storage systems like hydrogen electric storage, or ammonia have not been deployed at scale and has no cost history. I'm not inclined to gamble the future of civilization on technologies that we have zero experience building and operating.
By comparison, we have 70 years of experience building and operating nuclear plants. We only need to build 4 nuclear plants for each one we currently have to achieve a 100% decarbonized grid. The cost history of nuclear power shows a clear trend that serial production is cheaper than one off builds.
And you are incorrect about nuclear power not sharing components with existing applications. Nuclear power plants use steam generators, turbines, dynamos, and cooling towers. These are used in other heat engine based power plants.