Well you have to take something for a reasonable base, otherwise the argument becomes absurd quickly. We think of bare-metal (CPU-level) as our default base and

Well you have to take something for a reasonable base, otherwise the argument becomes absurd quickly. We think of bare-metal (CPU-level) as our default base and take that for granted. But the CPU itself has many abstractions over physics, multiple levels of caching, branching prediction, some built-ins and so on. A modern CPU sits much deeper in the skyscraper that you describe but it's still nowhere near ground level. Similarly, since with web browsers we get what we get, we might as well consider that our reasonable base for web development, it's not like anyone is going to do that part differently any time soon.