The number of racial categories would itself be an arbitrary limit not corresponding to actual genetic variance, nor would classification under such limit capture said variance, and none of it would match up to the folk biology of racial categorization. This is the general problem with reasoning backwards from 19th century gobbledygook about human genetic variation instead of beginning with the genetics themselves.

It may not be “your job” to provide such evidence, but you’ve made a series of specific claims about things like the rate of phenotypic variance among different racial groups. If you don’t want to defend them, that’s your prerogative, but you also can’t expect them to be received as authoritative or remain free of challenge.