But as said, IMO the DO will eventually be able to control those Powers better and more directly, making them less random. Likely he still won't be able to kill a certain person, but probably the DO will be able to concentrate his Powers more on certain areas, maybe through SH (e.g. if the Shadow attacks Lan's army or Caemlyn).

Besides that, things like the spoiling & rotting of food and plants, the control of nature or the increased vermin are obviously an expression of Randland turning to a world-wide Blight, so to speak (as e.g. also the beginning text of TGS by the unknown scholar shows). All this already affects mankind badly. It's e.g. said in TGS, ch.11, that the Saldaean soldiers become less effective because of the permanently overcast sky:

"The day was overcast, as usual, and the camp was subdued. Men who had bustled just days before — when the Aiel had arrived —were more lethargic now. The camp wasn't by any means unkempt; Davram Bashere was too careful a commander to allow that, wetlander though he was. However, the men did move more slowly. She had heard some of them complain that the dark sky was dampening their moods."

If the DO completely darkens the world into a permanent night, it will certainly demoralize people even more (as it is also indicated by the titles Towers of Midnight and A Memory of Light).