While the issue does exist for some, in many cases it's a lack of understanding in the mechanic. Whether you do or do not get hit is not exclusively related to the "red circle." The cast bar of the ability is what matters - if you are inside the "red" zone when the cast finishes, you're getting hit whether you stand there or are 40 yalms from the spot. You can see in a number of the Titan videos (some of them have been posted in this thread) that the player is clearly standing in the zone when the cast finishes. Understanding this greatly improved my gameplay.
If you start casting, aoe appears, and while you move out, surprise it finishes casting, you better instant cast RIGHT THEN, or you eat the aoe. Even if you were out when cast finished. Because your own cast screwed you.

So now casters have to wait until the boss aoes to cast (and for that you have to know the fight, or you waste a ton of GCDs more). Or they eat the aoe.

So in Titan HM, I go in the fight, Eye the tank. Then move until I see landslide anywhere. Move out of it if its on me, and THEN I have a window of opportunity to cast maybe twice...and I have to mentally discipline myself to always wait (I'm used to not wasting GCDs, not 'waiting so I don't die because of aoe positioning bugs').

Normal behavior I'd have: interrupt my cast and move out right off.
Behavior I need to have: not cast at all until the aoe is already there (and me not in it).