I worked in baggage for a while as a CSA. I saw more people have problems with their "high end" luggage than Travel Pro, Traveler's choice, Coleman, and other simular luggage that is use as our trade Bags. When a bag gets caught by a belt system, accidentally dragged, or something heavy damages it when things shift in the cargo hold in the belly of the plane, brand is meaningless. They all damage when s""" happens.
The reason why Southwest offers the brands they do instead of the high end brands is simple. High end or not, luggage is designed to protect the containts as it's only function. When the bag no longer able to protect the contains, then Southwest will provide a replacement or funds for you to buy a replacement. Not to mention, buying a high end piece of luggage is strickly voluntary on the passenger's end.