At the same time it happened, the french solar was 92% offline and the french wind generation was 81% offline.

Maybe we should get the opposite conclusion from this incident.

Based on yearly average capacity factor?

Since that incident storage has been scaling massively. How does a nuclear plant compete with zero marginal cost renewables?

https://oilprice.com/Energy/Energy-General/The-Quiet-Unravel...

by providing firm power.

Based on if it would run at full capacity like a plant would yes.

And no, storage hasn't scale at all yet, it would need a 100x increase before being useful for such events.

The proof is in the pudding anyways, if that works so well, why nobody does it?

Nobody does what? Solar installs are way way up.

Nobody does a storage based solar grid at a country scale.