That's absolutely true, if we're talking about individual mobility, but I was commenting on the idea of intergenerational mobility as mentioned in the parent and also in other places in this thread.
If your parent's economic position is irrelevant to your own, then every generation effectively 'resets' and there is not intergenerational mobility, which I took to mean as the gradual economic mobility of a family over multiple generations.
> A society where your parent's economic position grants a large advantage on you and your potential is inherently less mobile
While there is very likely a correlation here, most economists agree that economics in society is not a zero-sum game and thus one person's advantage as a result of their parents won't necessitate another's disadvantage to an equal degree. It's not a direct correlation; and that's before we factor in the increased motivation to innovate for your children's futures that come with an economic inheritance system, so on and so forth.
Less correlation between between your parent's wealth and your wealth is mobility, I think you're confused.
>As an example, your father could work hard and gain a higher economic position, but in Japan that advantage has a smaller effect on you and your potential.
Yes? That's a good thing, that means the society is more mobile. A society where your parent's economic position grants a large advantage on you and your potential is inherently less mobile.