IThey are the best dps in the game outside of assasins
DPS output doesn't matter one bit if you are unable to survive long enough to dish it out. I will furthermore point out that with the exception of shadows/assassins, melee tanks are literally the absolute worst tank in the game. Yes they can be used, but they have quite a few glaring weaknesses than vanguards do not share.
Furthermore, we can't use our dps when we're having to dodge aoe attacks in PvE or PvP. This game seriously favors ranged classes over melee classes in pretty much every area, and hiking damage numbers probably won't help things. The key issue is lack of ability to take hits.