Nobody says that overgeneration is free. But for example if your wind power costs are $20/MWh and your nuclear power costs are $80/MWh, even 100% overgeneration

Nobody says that overgeneration is free. But for example if your wind power costs are $20/MWh and your nuclear power costs are $80/MWh, even 100% overgeneration capacity for wind is still cheaper compared to the nuclear alternative. And if it achieves the desired effect cheaper than storage, then it will be preferred over storage as well. The optimal ratio of storage and overgeneration needs to be modeled for every grid independently; I believe the article I mentioned models it for the German grid. In practice, though, I expect that you won't even get energy waste from overgeneration if flexible energy consumers like BEVs or flexible hydrogen electrolyzers are connected to the grid. These will account for a major portion of electricity consumption and it will be possible to move their consumption around very considerably.