For those who think the latency only affects melee in pvp.
Every time you do an action (white hit, start casting, combo finisher, etc.), you need to add your latency to the animation.
Let's take a Fire of Ghenna as an example. It's a 2 second cast. Let's say it hits a strawman for 1.000 damage. Dps is the damage divided by the cast time, so it's 1000/2 = 500 dps.
But because of the latency, the real dps is lower. My ping is 320 ms so all my FoG will really take 2.32s to execute, resulting in a dps of 431 instead of 500. Basically, I loose 13.8% dps on that spell.
Now let's look at the instant casts, it's even worse. Iirc, instants are computed as 0.5s spells. For me it's 0.5 + 0.32 = 0.82s. That's a loss of 39% dps. And it's only about computation as the real animation is instant. A demo with no latency can cast 2 instants at the same time. For me, it takes 0.64s. It screws the rotations.
High latency makes it extremely hard to hit a moving target. It also makes it extremely hard to run off an opponent for the same reasons. But what most people miss is that it also reduces your dps a lot so yes, it affects pve as well. Dots seem not to be affected. I didn't noticed a big difference on my necro with 320ms and 100ms. Classes with a lot of instants or short animations are penalized the most. Last time I went to Europe for holydays I made a test on a strawman on my demo. About 1200 dps with 320ms lag and about 1600 dps with 100ms lag. Using the same character, perks, gear, and rotation.