That's a terrible argument that's often used to deflect from its crux. Of course within group differences are larger than racial differences. You're comparing a

That's a terrible argument that's often used to deflect from its crux. Of course within group differences are larger than racial differences. You're comparing a single (admittedly aggregated) factor to the sum total of human variation. That it has a lowered effect isn't surprising. Furthermore, the paper you cite doesn't even deny that different groups test consistently differently. Furthermore, it also explicitly states studies of test bias have consistently shown negatives. I also strongly oppose the conflation of population level metrics with individual level metrics.