The content is designed against Summoners. All the content in 2.4 and 2.5 require the ability to burst mobs down quickly and efficiently something the Summoner isn't good at. Also the new content is made so magic dps take care of AoE and melee takes care of single target again in area where the Summoner is lacking. At this point it's time that SE reworks the Summoner to fit into the content they are designing.