I'm not up to level 50 yet, but wouldn't some of those problems be solved if people obsessively grouped more? If you see someone else standing around for the mob, give 'em a /wave, then send them an invite. Then you wouldn't have any problems with "other people" jumping in and dealing damage which apparently makes some mobs not drop their item.
It helps a little, but not enough. You still have two groups fighting over 4 NPCs for 3 items each. And like I said, sometimes the NPCs won't drop and sometimes interference affcts a drop. So you still have things not working at optimal levels, even with grouping.
They could kill 2 birds with 1 stone and make the outside mobs add to the quest (Drops and Kills). At least then it wouldn't be so annoying to fight them all because you'd be working towards your goal (Like in Black Hole).