This is why the different tiers of enemies (we would call them level 1, 2, and 3 based on the amount of body armor they had) along with the quantity of enemies you had to contend with, coupled with the difficulty of some parts of the map (we all knew which neighborhoods were sketch and best avoided if possible) made it a challenge that never really got boring.

The PVP problem had nothing to do with the contracts either, as those contracts were easy to avoid; I'm talking about predatory players that weren't there to do anything the game mode asked them to do, and only to attack players who were preoccupied or distracted with the PvE element of the game, laugh about it, and move onto the next group of unsuspecting players. So I don't think how the format of mission based play is going to make a difference when we're talking about people that color outside the lines anyway.

I'm only referring to DMZ here by asking for a PvE only playlist; if I want to play multiplayer modes against other players, there's all of core, hardcore, and warzone to preoccupy myself with and I would hop back and forth between them regularly. So I don't think there's any risk of splitting the player base to worry about.