That must have been one of the worst DF articles I've ever read.
Chaotic A2 overground encounters? What? No one cares about story/campaign performance. You will be playing this for maybe 4-5h if you haven't played the story before. The majority of this game is playing in parties and clearing Rifts and Bounties. Even while leveling up. As long as they don't test the performance in those cases it means nothing.
This is how a normal 4 player Rift looks like in most of the encounters (just a quick find on YT - I don't know who the guys playing are but it is a decent representation of how the game looks most of the time for everyone who's never seen it):
https://www.youtube.com/watch?feature=player_detailpage&v=Xrc5NuG-EpI&t=495
This is the time when you want a solid framerate to be able to dodge and react quickly. All this talk about some dropped frames in desolate and barren areas while running around with a Barbarian and pummeling enemies without any full screen spell effects is REALLY conclusive. Thanks, DF!