I think the best way to look at it is time spent and speed of kills. Take the current mars strike for example. mars foes seem harder to kill for most at the same level. Think about it this way: The time saved racing thru the strike will get you far more kills for your time in other areas of the game than the kills you will get against lvl 25 guys. As far as we know, drops are the same regardless of mob level. unless this has changed? Also, if you want to talk with your fireteam members, it takes two seconds to create a party and invite them. be proactive. I bet most gamers will help you kill extra enemies if you ask, I know I would.