Feel more attachment to your Conjurations. Be able to modify the abilities they have. Be able to control the actions they take better with a true Pet Command system. Having certain Conjurations out would do certain unique things if invested. The fact of the matter is that the Perks in this game are not utilized properly. There is a LOT that can be done to make Conjuration more engaging and interesting. Take other games where you can summon or conjure: Magicians, Necros, and Enchanters from EQ1. Warlocks from WoW. Golems, Skeletons, or Reanimations from Diablo. There are so many examples of things that "could" have been borrowed or improved upon to make a better Conjuration system.
Agree that they could have given special abilities to the summons when you take certain perks. 50% more powerful is too vague and not quite exciting compare to special skills.
For example, fire elementals could have 50% chance of rebirth upon been killed. Frost elementals could be more powerful at start but gets weaker and SMALLER as their health depletes. Lightning elementals could teleport like a boss. And finally instead of daemora lords, maybe they should have blood golem/elements as the final elemental summon which absorbs health with their attacks and upgrades allows them to transfer health to their caster if he has taken damage.
As for the summoning of necros and warlocks, no. Summoning of humans with intelligence and binding them to your will is clearly a deity level skill. In theory, there should be no reason a random conjurer NPC can't summon YOU and force you to fight and die for them if that is the case.