For average players the DoT system causes a lost of 30-60s dps because their damage ticks as one massive DoT on a global timer instead of each DoT having it's own damage tick and timer. Also Summoners initial damage starts of high but quickly drops off after 4min because of potency issues and how SE designed the DoT system. The Summoner is in the Saboteur slot which involves weakening enemies to increase party DPS but they are treated as pure DPS. These issues all combine to make the Summoner a sub par DPS.