Summoner as a sustained dps is a myth that players perpetuate. In long fights the Summoners damage starts off high then declines over time because of the diminishing returns built into a DoT dps. The Summoner has the same problems that the WoW Warlock has it has decent damage but can't keep up with other dps classes in high end raiding because their damage declines over the course of long fights. DoT classes best specialize in crowd control and they are also great when combined with restorative buffer like the Scholar but as a dps they suffer from the power creep, stat scaling and declining damage over time.