While other methodological aspects may be more doubtful, in the paper of Talhelm of Dong there was no "ideographic vs alphabetic" problem.
That paper compared Chinese people with Chinese people, where both groups had been assigned randomly and forcibly by the communist authorities to become agricultural workers in wheat-cultivating regions or in rice-cultivating regions.
The only confounding factors could be other geographic differences besides their major crops.
The point of the paper was to exploit this unusual historical fact as a social experiment that has eliminated most confounding factors that exist in other comparisons, like the factor mentioned by you.
It turns out this paper from Talhelm & Dong supports its methodology by citing a paper by Talhelm et.al. and one by Dong et.al.