Sorry SE, but endgame won't work if you don't fix something.

[Cienna]

Is this really a latency issue? Or just a failure to understand the mechanics of how the aoe system works in this game?

The game determines if you are "in" the area by your position when the casting bar is 100%.

Here is just one of the MANY video examples in this thread.

http://www.youtube.com/watch?v=QsHuXAl-bOY

At 6:21 landslide cast begins
At 6:22 player leaves aoe with cast bar at 75%
At 6:24 player is hit by landslide and knocked off

They were out of the red area well before the cast bar finished. They still get hit.