It’s really a shame that this subject can’t usually be discussed rationally. I find it quite interesting.
I believe that every group and subgroup you can create will have certain strengths and weaknesses when compared to other groups. Isolate the two groups long enough and those strengths and weaknesses will be amplified through the generations. This doesn’t mean one group, breed or whatever is superior, just that they have some things they are strong at and others they are weak at relative to other groups.
Even within the same family individuals can have massive differences in abilities and aptitudes. Two of my children are as different as different can be when it comes to their strengths and weaknesses. Give them mates with similar traits and isolate them and their descendants for thousands of years and the resulting populations would still probably show similar strengths and weaknesses as the original two siblings in my opinion.