Well to be honest, that's what I assumed the summoner job would be... Using other enfeebling and DoT magic to build up a damage meter (like a LB meter only solely for the SMN) and then when it's full they get to call the summon to perform one massive attack. So basically what they are in the single player games. However I do understand how this can't really work in an MMO setting.
I'm not a summoner myself (would like to eventually level it) but I can see how I'd be disappointed if I wasn't required to summon a full size primal in a group or FC. But personally I don't see SE putting in that requisite somehow...
