Nuclear is expensive, and you can't shuffle that expense around under three walnut shells hoping it will somehow disappear.
You're playing with apples and oranges. You want us to look the other way while all the exotic things done to fill in for renewable supply/demand mismatches are not amortized over a tiny number of hours of operation, but want to point to the same problem with nuclear.
A diversity of power sources, each with their own problems (cost [nuclear/storage], invariability [nuclear], volatility [wind/pv], total resources available [hydro/geothermal] is what will get us through this. Especially since we're really maxing out what we can do with wind and solar and it's not going to ramp high enough in time to save us.
France's past system is irrelevant, since it was built at a time when renewables were completely noncompetitive. The world has changed now, and changed radically. Going forward, France will be going renewable too.
Sure, it's expensive, but all the things we'll have to do to have an all-renewable grid are pretty expensive themselves and unproven.
Yes, we should end up with a much smaller mix of nuclear than France had, to help optimize cost. But it is an option available now that we know will work, and I believe that the optimum point is not 0% nuclear. (In western democracies, though, nuclear has become practically impossible. This hasn't stopped a large amount of reactor construction in China, so obviously planners there disagree with your assessment).
Further, nuclear and wind are comparable in CO2 emissions, and PV is a few times worse. So if we really care about minimizing CO2 there will be some nuclear in the mix.
Betting everything on power->gas->power when we have basically no evidence that this will be economical at scale is crazy. Betting on pumped hydro or battery storage is also dubious. We should be pursuing all avenues available to us.
Also, making a pure opportunity cost argument is a little weird as well. The investments are not purely fungible. That's why we should both give extensive resources to ramp PV and resources to ramp nuclear and resources to ramp p->g->p, because they're not the same resources.
It is not an option we know will work. The inability of France to replicate their previous putative success means we can't take any of that for granted.
We have evidence that nuclear will NOT be economical at scale. The evidence is there in a cavalcade of disastrous experiences, even in places like France were experience supposedly, by your reasoning, would have told us to expect otherwise.
Then you size wind and solar for the remaining 70-90% of load, say 70th percentile.
During the remaining 30% of the time, you use agreements that allow you to shed load and you draw upon intermittent hydroelectric resources.
The solar/wind overcapacity factor and the remaining bit of battery or power->gas->power you need can be much, much smaller because the reliable nuclear base load really stretches the hydro and load shedding.
And you can use the "extra nuclear power" when wind/solar are overproducing to pump hydro, charge batteries, or make gas for power->gas->power.
Put another way: the reliable nuclear energy just subtracts a constant amount from grid demand, and the remaining wind/solar production variability is reduced proportionally.