That model of efficiency (RAM and CPU time) is based on classical computation. When your underlying model of computation is full quantum computation, it's simp

That model of efficiency (RAM and CPU time) is based on classical computation. When your underlying model of computation is full quantum computation, it's simpler to just run everything at once. It takes no energy if you run everything without picking out a scenario (but in a kind of "tree falling in a forest" way), and more energy if you select out specific scenarios to look what happened (I/O is expensive). Counter-intuitively, the computation part of quantum systems is free in ways that we consider classical computers expensive to run. It's reversible and doesn't consume any energy. That may seem like it's avoiding the point, after all what does it take to run the "underlying model of computation". But what I'm trying to say is that "quantum all the way down" (see also turtles) is as much a valid model as "mechanical computation all the way down", which your picture relies on. Neither of them is more fundamental. It may seem like quantum-all-the-way-down is a bit artificial, because we can in principle run quantum simulations on classical computers, which seem simpler. But it turns out we can't. There is a fundamental intractability barrier for simulations above an arbitrary tiny size, which means we can only simulate interesting quantum systems using other quantum systems. It really is quantum-all-the-way-down. If god came up with the quantum-all-the-way-down version, I'd say that's pretty clever, because it's way more efficient than anything you would implement, with your old-school classical RAM and classical CPU.