For me the issue with them is primarily one of flavor, they simply do not feel like Final Fantasy summoners, they feel almost exactly like Warlocks from World of Warcraft. I would have much rather seen a class whose damage primarily came form the pets with the summoners personal spells being about debuffs and supporting the pet/party. Summoner in its current implementation feels functional but a touch on the weak side, I ended up switching to black mage after getting to 31, a decision I have not regretted. DPS wise I think the two classes are fairly equal, but the summoners lack of burst can be a seriously liability when there are adds that need to go down in short order especially since they do not have access to sleep. I feel much more useful to the group as a Black Mage overall.