Let's compare the largest pumped water storage plant in the world - Nant de Drance in Switzerland [0] - with reactors at one of the largest nuclear plants in the world - Hanul in South Korea [1].
Nant de Drance has 900MW of storage, and took 14 years to build. Each of the last generation reactors in Hanul generate 950+MW of power, and took 5 years to build. The first newer generation reactor is 1340MW, and (assuming it keeps its schedule) has taken 10 years to build. They've done the first tests so they have some chance of connecting to the grid this year, but let's be pessimistic and say that it will take another 4 years - matching the construction time for Nant de Drance.
That's still ~50% more power, and it is actually generating it: for Nant de Drance to help, it also needs >900MW of actual renewable power generation plants to be built and operated.
There is little economy of scale, in pumped hydro. California stores a much larger amount of energy in numerous reservoirs all over the Sierra Nevada range.
Nant de Drance has 900MW of storage, and took 14 years to build. Each of the last generation reactors in Hanul generate 950+MW of power, and took 5 years to build. The first newer generation reactor is 1340MW, and (assuming it keeps its schedule) has taken 10 years to build. They've done the first tests so they have some chance of connecting to the grid this year, but let's be pessimistic and say that it will take another 4 years - matching the construction time for Nant de Drance.
That's still ~50% more power, and it is actually generating it: for Nant de Drance to help, it also needs >900MW of actual renewable power generation plants to be built and operated.
[0] https://www.nant-de-drance.ch/en/the-plant
[1] https://en.wikipedia.org/wiki/Hanul_Nuclear_Power_Plant