Guardians can be very good, Vanguards can top charts. Only problem is both of them require guards because the vanguard has no threat drop, and the guardian has a terrible threat drop, the only threat drop in the game that actually costs resources.
Funny that, i personally think its ruddy brilliant. Granted, it does cost resources, which makes it cumbersome to use. The perk of it however is the fact that if you use that thread dump and still have aggro, taking dmg will reduce it further. however, the best thing about it is the fact that its actually useful outside of a PvE environment, as its use in PvP is really quite nice.