Although I would really love to see this drop system implemented too, it is literally impossible de satisfy everybody.
If the drop rate is not altered enough and tends to favor multiplayer even with low players then ironically, it favors back playing alone because you had better play "with yourself" than "noobs" as they won't make your run that faster (not to mention if they even slow it down with deaths and DMC) so you dual (or quadral) log to increase the chance of drops.
Even if the IP check is implemented, you could still ask people to join your room at key points like before Saint Million fight so they help you have more chance to get the drop for free exp.
Also beginners will only want to play with pros : do nothing, get free exp, have as much chance as someone who worked hard to get an item. Nice isn't it ?
You have to keep in mind that when you play with weak players, you are here to help them and/or have fun at first. You can't expect them to help you if they are indeed weak.
It is the logic of most of multiplayer games. You are in a weak team > you have an handicap. And this is normal.
Either way, whatever is done, there will always be remaining issues somewhere.