You've calculated instantaneous power output under optimum conditions. That will drop when the conditions are non-optimum, such as at night. Unless you have some kind of humongous, super-efficient storage system, which will add significantly to costs.
Also, I doubt if such a system will have much in the way of dispatchability. Something spread out over that much territory, even in the desert, is bound to have some measure of variability. And variability is something you don't want if you are sitting in the hot seat of the regional power dispatching center.
The variability of power on a solar cell is why you take the “peak watt” value but only consider 5 hours per day of sunlight. Obviously there are many more hours than that of sunlight, but the 5 hour figure is a way to average the efficiency over the whole day of weak-strong-weak insolation.
Yes, you would have environmentalist opposition. But that wasn’t the original statement. The original statement was that if the entire state of Nevada was covered with PV, it would barely power Las Vegas. That was an exageration. There are over 109,000 square miles of land in Nevada, and using only 10% of it would more than power Las Vegas — it would power all of Nevada and several other states.
Its variability means solar PV can never be alone, but storage doesn’t have to be in electrical form. Imagine you had unlimited cheap solar PV electricity. You could combine that with hydropower by using the solar PV to pump water from a lower reservoir to a higher reservoir while solar was available and let the water run through the hydro system at night. Or you could set huge flywheels spinning and let them drive generators when solar was unavailable. It doesn’t matter how inefficient any of those cycles would be, only that the total average cost works out.
This is actually a pet peeve of mine. People write articles about how this or that needs to be more efficient, when efficiency is irrelevent. What matters is the cost. Having solar PV cells that are 30% efficient but cost twice as much as others that are 15% efficient is not really progress, because the 15% cells are already more “efficient” than necessary in terms of area available vs. area needed. We’d be better off with 15% cells that cost half as much, or even 10% efficient cells if they cost only a third as much.