If we kept the same languages and made japanese people write it massively in 26 half sound symbols and made all of what you call a white european population use 3k+ ideogram drawings for word starting at 3 years old, do you think we d see exactly the same performance ?
I bet you the writing tradition is very influencial when it varies so much and has no relationship with language, especially in Japanese where they frankensteined Chinese symbols over centuries which must require an enormous mental gymnastics and redirect large processing power vs someone who can read and write everything he hears relatively simply?
No, neither.
> If we kept the same languages and made japanese people write it massively in 26 half sound symbols and made all of what you call a white european population use 3k+ ideogram drawings for word starting at 3 years old, do you think we d see exactly the same performance ?
Yes, the influence of spoken and written language appears to be zero. I mentioned this.
Japanese people show extremely high performance at "spatial awareness" tasks compared to whites.[1] So on average this isn't true. But it's true that there does not appear to be any benefit from either language -- Japanese-speaking Japanese show no advantage over English-speaking Japanese.
[1] On white-normed IQ tests, East Asians generally show a bit of underperformance (relative to European whites) on verbal tasks and gigantic overperformance on spatial tasks, which is traditionally averaged out to an average IQ score moderately above that of whites. Interestingly, Native Americans show the same slant -- much much stronger spatial than verbal performance -- but at a lower base level.