But then Azzy could apparently pop in and out to bestow his seed upon the world at intervals because reasons? Did he ever bring any of his kids back? If so how does that factor in to the concept of a closed population?
But anyway, absent his mutation, Kurt's a light-skinned dude of complicated parentage raised by Romani stereotypes, and his mutancy and background are always going to be so much more a factor than his race that I don't know that it's worth doing more heavy lifting trying to figure out the ramifications of an incompetently-plotted storyline than the writer himself seems to have put into creating it.