Your reasoning is exactly why I loathe any step towards this sort of thing in the UK. You cannot infer disadvantage from a simple racial categories. For example, the majority of South Asians I know in the UK have affluent and/or well educated parents. On the other hand I know there are people whose parents were poor educated, spoke English as a second language, went to schools in bad areas, etc. If you try to balance by ethnic group its the former who will get the most advantage from it. The Asian side of my ancestry was both more affluent, and had more people go to university than the white side.

As the article says the best universities here look at predicated A levels grades, their own admissions tests, and interviews. From what I have heard at open days etc. they are often clear that they do not care about ethnicity or skills at sports.