What you're missing is nuclear is too slow to spin up! We simply don't have time. We need to cut emissions 50% in 10 years, and nuclear is not going to get us there. Look to other renewables.
You're assuming that we only need to replace all our energy sources with renewables but otherwise we can keep running as usual.
As you correctly point out, that's not going to cut it. However, there's an easy solution that has been suggested by various people for at least the past 50 years: Lower consumption, lower energy requirements, halt the desire for infinite growth.
The richest countries are the biggest polluters per capita, no competition. Accusing the "Indians and Chinese" for pollution which is in fact the direct consequence of "Western" consumption is misleading, hypocritical and redirects attention from the real, underlying problems.
See also [1] for a counterpoint to your claims of increasing efficiency.
No argument at all about per capita energy consumption. My point isn't to blame developing countries at all. It's to illustrate that as over 2 billion people try to emulate Western lifestyles, their energy consumption is going to skyrocket. And Western expectations that they should just limit their growth/advancement is the hypocritical view.
When you view Western energy consumption, it's growth is largely correlated to population increases.
Of course they can. It doesn't take more than 2 years to setup a solar/wind farm, meanwhile a nuclear plant takes an average of 7 years to build and deploy.
Solar is especially good at this, because with the right incentives you can have people put it on their roofs - it's the sort of scaling that's impossible to achieve in megaprojects like nuclear power plants.
Rooftop solar isn't viable in a large portion of the world, and solar is much better served in mega deployments. Scale matters.
That said, if you look at the total amount of energy consumed worldwide, the grow rate of this energy consumption, the amount currently generated by renewables, and the growth rate of renewables, it's pretty obvious that there's no realistic way to cut emissions 50% in a decade. Absolutely none short of a global war that devastates both modern society and reduces world population by 25%.
If we had the will, there would be ample time. If you look at humanity's achievements, a full-court-press on this problem though multi-faceted technological investment is well within grasp.
However, that framing is de-emphasized in favor of politicizing the issue, imposing guilt on those who consume resources, and trying to alter the way billions of people live through coercion or decree.
We're screwed until the modern-day luddites yield that all of humanity wants, needs, deserves, and can sustain effectively endless economic growth and prosperity as long as the universe's limitless resources remain uncaptured. To think that at this junction we should consider the boundaries of human activity are now fixed is to just continue the endless tradition of doubters and cynics who have lacked imagination over the centuries, and held back all good things.