My understanding, and I've read a fair amount on the subject, is that geography for pumped storage is actually pretty limited compared to the eventual need. Do you have a source for it being plentiful?

Promising alternatives to mitigate solar and wind variability, aside from pumped storage and nuclear, include advanced geothermal, load management, thermal storage, long-distance transmission, storing clean hydrogen or clean methane (made from electrolysis and captured CO2), and possibly long-term battery technologies (not lithium, that'll mostly be for overnight or shorter). In no particular order.