I strongly disagree.

You put together a strong argument. I think that this will depend on which genes we examine; if there is some intelligence-boosting gene that most Xs have and most Ys do not, then the effect of that gene will be more noticeable when we do race comparisons than economic status comparisons. However, intragroup variability is higher than intergroup variability, which suggests that for every intelligence-boosting gene like that there should be at least three which aren't strongly associated with race, and if we accounted for all the genes then the intelligence-economic status connection would likely be stronger than the intelligence-race connection (though I have insufficient data to conclude it would be stronger).

I was thinking about the first kind of genetic effects only, since they seem easier to find and study than the second, but you are right to question that choice.