>societies where laws are supreme (no-one is above the law), and where the same crime results in the same sentence, no matter who you are...

If that's the definition then, um, yeah, I think "bell curve" is a very diplomatic term for the de facto reality in Western Nations. In fact, I'd go so far as to say that the de facto reality in all nations, Western or not, falls well short of this rule of law ideal.

I've no evidence to support the following suspicion, but I think whenever humans are involved in a system, all of those well known human failings we have are going to manifest themselves in that system's output. I don't think there is a way around it actually.

In practice, there probably is no society governed by rule of law if equal treatment is going to be your measuring stick. I honestly don't think such a place exists.