ULCC and LCC are different things. Southwest's model is hard to see now because the majors so effectively copied it. Southwest used to get mocked for only serving peanuts when all (7) mainline carriers were serving hot meals in coach. There's the famous delta cost-saving story where an FA suggested they remove the decorative lettuce leaf from under their coach entrees and it saved a million dollars a year! That was the regular cost model against which "low cost" was compared.

The ULCC unbundling of luggage and such luxuries like airport-printed boarding passes was not a Southwest model.