Well if we sit and think for a moment, we can see that this probably isn't true. Remember how Bungie was setting this originally in a more "Fantasy" setting then a Sci-Fi Setting? Well if we take that nugget of truth and think about the word Vanguard for a moment. Vanguard comes from the medieval formations within their armies. They were made up of the Van the Mid and the Rear. The Van or Vanguard was the front or first part of the marching order. In most "fantasy'" books i've read this held your most powerful and trusted and best warriors. In real life this had trumpeters (To proclaim the coming army), engineers or workmen (to clear a path for the baggage and siege weaponry.) and people to accept and summon any town or castle's surrender. So, armed with this knowledge, I would say the Vanguards are probably not a class but a group within the Guardians as others have expressed here. It also doesn't make much sense within the constructs of the classes already present. Titan - Badass soldier Hunter - Badass scout Warlock - Badass commander