Anyone who gets into a top tier school, by preference, legacy, or whatever, is already on a course to do well. They could have settled for the 2nd tier just as well.

The different perspective you are referring to is groups versus individuals. to the degree that they differ, whatever is most fair for one will be less fair for the other. It is objectively true that a group preference will be unfair on an individual level to some people. For example, on an individual basis, legacy admits only benefit legacy applicants. Yet you're using this argument to support penalizing people who are not legacy applicants.