I wonder if maybe there is something in between, that would serve well? While it is a good thing that noone can steal your rewards, or leech on the work you've done before striking the killing blow and reap the spoils, it is frustrating not being able to help others in a fight. Unless you are a healer, there's no way to aid others you pass who are about to lose a battle. And I've always enjoyed that about online games, to lend a hand occationally.

So how about if you target and try to attack someone else's monster, that player will get a small notice in the corner (one that doesn't annoy them while fighting by flashing over half the screen), where they may choose to allow you entry to the monster. And if you do, you only get half the rewards you normally would, and they still get full reward.

Or something like that?