> in theory any amount of power a nuclear plant would generate could also be achieved with large amounts of renewables no?

You're exactly right, in theory, in practice it's impossible without some significant amount of energy storage, which we don't really have.

I once did this calculation for fun: in Italy, starting from the current energy mix and replacing fossils with more solar while meeting the demand in winter would require covering with panels an area equal to the region of Abruzzo (that's like 5% of Italy's total surface).