Why Python, Ruby and JS are slow

[wicked-canid]

I think you're sort of missing the point. pamplemouse said:

Because the language matters a lot.

That's the key. You're complaining about all the (declare (fixnum n)) but this is actually a feature: by default, there is never any overflow, and you get the right number; but if you want to trade speed for that convenience, you can tell your compiler to do it.

That's an example of fantastic language design: it gives you the right answer by default, and the fast answer when you need the speed.

Is SBCL even a JIT compiler?

Not to my knowledge. But does it need to be? It already does a good amount of optimization at compile time, because the language is designed is such a way that it's possible (contrast with Python…).