No. The ration killing/revival items is the right one. The cooldown is also the right one. Reviving items have 1 month cooldown. Killing have 2. There are how many? 4? 5 killing items? And probably 6 or 7 revival ones (thanks to Nimmy and her quest). I REALLY don't see an unbalance here. To be perfectly honest, there are too many reviving items for my taste (remember there are also one time revivals out there!).
Now, about Eon's contract: it takes 2 to tango. Eon will kill if only hired. Even if he'd want to kill just because he hates someone, in theory, he would not be able to. He has a role, he was given an item to support his role. Imo he's doing a great job but this is really not the discussion here. Let me take this a step further: who are the people that get killed? I can say without being afraid of making a mistake that popular people get killed (doesn't matter what kind of popularity - bad or good). And let's be honest: ALL popular people have at LEAST one friend that can help (and by help I am covering all aspects: friend can fight, get some reviving items, can pay for reviving items etc etc). NOBODY kills noobs just because they can because is really a waste of a good killing item.