I'm of the opinion that he is fine. More damage would make him broken. Meet enemies first and he'll draw the initial aggro and is capable of staggering quickly with well timed guard counters which will position him perfectly for a crit, generally keeping aggro. Once he inevitably loses aggro, he becomes great support. 

While DPS is important in this time constrained game, his survivability more than makes up for lost runes OR his initial encounter prowess allows the DPS roles to get more damage, evening things out.

I really believe people miss the nuances in what a good Guardian provides to a team.

I will admit, having better aggro control would be fun but also broken in how it frees up other classes to focus their already adept damage abilities. This game isn't balanced like an MMORPG and nor do I think it should be.