All of what you said is true, but are American Eagle, Gap, Abercrombie, H&M, Uniqlo, and Old Navy sufficiently unique from each other as to justify all of them

All of what you said is true, but are American Eagle, Gap, Abercrombie, H&M, Uniqlo, and Old Navy sufficiently unique from each other as to justify all of them having floor space in the same mall? Not really. Two or three of them makes more sense. Your point holds up well for stores with higher-quality offerings (e.g. Nordstrom, J.Crew, or Express), where it's always worth your time to shop around, see things in-person, and try them on. Of course, some clothing stores have a more narrowly-defined target demographic, and thus they are immune from fast-fashion redundancy (e.g. Torrid, Hot Topic).