Speaking as a full sunwell tank, I can completely confirm everything that Xav has said here.
The issue wasn't so much that the DPS can't control themselves so much as that the fight doesn't ALLOW the tank to generate less threat. It's a constant strain from start to finish in sunwell to keep threat on mobs that do everything they can to counter your efforts.
Cleaving mobs, stunning mobs, mobs that teleport, mobs that fear, mobs that stun AND fear! Bosses that can and will gib you when even a single debuff is missing (brutallus).
Even simple things like reflections tanking for kil'jaeden is significantly easier. Warbringer is AMAZING for this.
In relation to how it is now, I've done several instances so far in the new patch. I did well in sunwell, getting 7-10th on the damage meters in general. In ZA and KZ however, I was number 1 or 2 the whole run, usually ending with about 15-18% of damage done (full T6/sunwell geared groups).
In reference to people saying that the aoe damage is too much. I strongly disagree. You can't hold using aoe abilities against single target threat, so it's important for dps to focus as well. And some things just can't be tanked in large numbers/full pulls. I would enjoy watching you try to tank full pulls of trash in sunwell past twins. That'd be funny.
To be perfectly frank, if you haven't been tanking at top tier content there is absolutely no way for you to conceptualize the problems that were rectified by the changes to threat that they made. Did they go overboard? I don't think so. I still have people that can keep up with me on threat in certain instances. But modesty aside (and I'm sure any MT in a full SW clearing guild can say this), I'm extremely good at threat, and tanking in general. Some of my DPS are extremely good at their jobs too, which has the end result of generating a lot of threat. If you think you can just slack while tanking still, then you're wrong. There's still a component of skill required to stay ahead of skilled DPS. If you're finding it boring/easy to keep threat, then your DPS needs to learn how to step it up, for sure.
And besides, boredom is a function of personality, not a response to stimuli, and the tanking rotations are much more interesting than ever before!
"He who fights with monsters should look to it that he himself does not become a monster." -Frederick Nietszche