@Seelenernter: i used my summons even in the last fight. Maybee they are weak but they are very cheap to cast (and has nearly no cool-down). Every char in my group was able to cast a summon (either pet, spell or scroll).
Having up to 4 additional chars on the battlefield simply outnumbers the enemy in most situations plus you can summon them anywhere you want. Thats a very effective crowd-control. Additionally all elementals left a "elemental" area effect while dying, whats pushes the cc-effect even more.