Astral Codex Ten (or Slate Star Codex, or,...) would be a lot more compelling if one didn't always find some obvious historical error like this in the typical article. If only he could afford a fact-checker.
Dresden, Tokyo, Hanoi—how many more counterexamples do you need? The means to level a city with conventional bombs already existed. The nuclear bomb's innovation was as a weapon of intimidation, not raw destructive force.
Conventional strategic bombers and high explosives would never have given us MAD. The raw destructive force is absolutely relevant, it was (and remains) infeasible to do anything like wipe out a whole country in a day or two with conventional weapons, that'd take months or years and enormous dedication of resources. With nukes? Now it's possible.
I'm really not getting the reading of this as "LOL we could blow up cities with regular bombs, he's wrong!" Like, WTF was all the worry over nukes in the cold war, then? They're extremely obviously a major game-changer. A functioning nuke program means multiplying the max plausible destructive power a country can deploy inside a week by a very large number—no later developments in conventional weapons have really closed that gap, it's a whole other category of weapon, and you either have it, or you don't.
Unfortunately, public intellectuals in our current society don't hold themselves to these kinds of standards (which would have been considered obvious for public intellectuals a couple of centuries ago), and no one else holds them to it either.
Have you read anything a couple of centuries old? The problem was, if anything, much worse!