The new smaller proposed modular reactors are capable of ramping up and down energy output in a way they could replace natural gas powered plants.
If nuclear reactors are downsized, electricity prime costs will normally rise, because the small reactors require the complete infrastructure (Transformers, emergency power supply, safety measures,...) of large plants.
Electricity from nuclear power is already extremely expensive and non-competitive today. This is also evident in the predictable disaster of Hinkley C in the UK:
Sourceinitially estimated that electricity could be produced at the competitive price of £24 per MWh.
SourceThe deal he refers to is the so-called Strike Price for Hinkley C's electricity. Also in 2016, the British government fixed that price at £92.50 per megawatt hour (MWh). The price rises with inflation and has now reached £106/MWh.
Back then, the equivalent price for electricity from offshore windfarms was well over £120/MWh. But wind costs have fallen fast. Today new wind projects are fixed at about £50/MWh, well under half the price of Hinkley power.
Source was from 2021, the current guaranteed purchase price is now likely to be 120 pounds/MWh because of inflation.
By contrast, the prime costs for solar and wind power, as well as the price for energy storage, continue to fall.
As you yourself write, these are "proposed" reactors that exist only on paper. By 2050 at the latest, energy production must be largely CO2-free, and new, small nuclear reactors, even if their construction is decided today, can hardly make a contribution, since it will take too long to build them en masse.
That is, even with the additional cost of energy storage, the prime cost of solar and wind power are cheaper or at the same level - e.g. prime costs for wind 40-80€/MWh onshore and solar 30-50€/MWh in Germany.