I think you're still missing what I'm saying. Yes, running a grid 100% on renewables is probably extremely difficult. Yes, nuclear may be the optimal way forward today. But I still think the most likely outcome is the renewable grid anyway.
Why? Because there's no "we". There's no central planning. What there is is a bunch of self-interested parties that don't care about the entirety of the problem. Everybody will go with what makes the most sense to them, the result will be suboptimal, and then once things go wrong the country will have to fix the problems somehow.
Your plan may make sense in China where the government can indeed implement a central plan, costs and opinions be damned. But it seems extremely unlikely to happen in most western democracies because the politics won't support it.
"Yeah, that's why there's no plan to actually decarbonize with renewables."
What I'm trying to say is that there's no global plan whatsoever. In most countries we don't have the ability to implement any kind of comprehensive central policy. We have multiple parties that can nudge things in one direction or another but none of which has full control over what happens.
"Pass a carbon tax such that building a nuclear plant is less expensive than running solar during the day and natural gas at night."
But the problem is that there's no single party in charge of solving that problem. You pass a carbon tax. Fossil fuels die. Companies will build solar, because it makes them money. Companies won't build nuclear because it's expensive to build and solar is eating their lunch. The powerplant building company cares nothing about the economics of keeping the country powered 24/7, they care about the economics of building their plant. If their business model works okay while selling nothing at night, then it works, and that's that.
Then we'll get blackouts at night, solar companies will shrug "not our problem", and the government will have to scramble to find a solution.