I agree with the criticism of being split off from your friends due to them being a much higher level, it kills any social apect of the game other than being in a party chat together.
Its not that much of an issue. You can all play together again once you hit 30. Its only really an issue if some of your friends rank up faster than others.
I understand why they don't let you in the dark zone with two big a rank difference, and it does let you join missions, it just scales the mobs to a level somewhere in-between the bottom and top ranks.
I think they've done all they can given how the game works. Imagine if yo could join the level 14 darkzone at level 30 by joining on a friend .....

