Perhaps it will be expanded later? Also, you do get a wide variety of skills to go on your limited bar, so despite having one weapon, you get a variety of ways to use it. On top of that, there are sub-weapons, not necessarily used as equipment, but they tie into your skills. Espers have all of their cool illusionary projection attacks, Warriors have spinning sawblades and an arm cannon, Stalkers have traps like proximity mines. You just pack one main weapon. Maybe there are more, I don't know. This is just my two cents.