Vanguard, even if specced as DPS, was never meant to be a true DPS. They created two archetypes, the tank and the DPS for this reason. You can get higher DPS with using a DPS spec, but you should NOT being out DPSing a DPS class who is specced for such, assuming they are players of equal skill. Your DPS specs are an added/off DPS.
With that said, if you're guarding someone of importance (i.e., healer or DPS), then your procs should be going off OFTEN. The guard absorbs half the damage that the person being guarded takes. I've never EVER had an issue with this.
See the above two points and if you're still not happy, then feel free to roll the class you want to be: DPS = Commando or Smuggler. Otherwise the others who say "you're doing it wrong" are correct. Just like real life, not everyone is good at everything. Sorry, but that's the truth.