Short version, no, it's not.
I know that a LOT of people out there struggling on titan hm complain about lag, especially with plumes. I know there's a video out there that shows the person is out of the plume for ~1 second and is still hit by it. It must be lag, right?
No. That's not how ff14's aoe's work. In the video I just mentioned (which can be found here), it does indeed appear that the person WAS out of the plume. But, for those of you that know how ff14's aoe's work, you can plainly see if you pause the video at the right time, that person was NOT out of the plume.
For those of you that don't know how ff14's aoe system works, you're basically dodging warning indicators, NOT the actual aoes. If you're still in the aoe indicator the split second the aoe is done casting, you are considered standing in the aoe, and you will take damage, along with the other effects of the aoe. If you are still standing ANYWHERE in the plume the very second it finishes casting (which is slightly before the plume warning indicator starts to fade), you WILL get hit. It's not lag, it's just the way the system was designed.
Now, for those of you still stuck on titan hm, I'm not sure how much you've researched the fight, but there's a very easy way of avoiding most of titan's aoe's! It's very simple, and it's called "moving ahead of time". For example, when titan first transitions into phase 2, run a little bit and start dps'ing, right? No! Keep running, because titan's first move is a plume! If you're running when the plume happens, not only does the center of the plume start ~.5 second behind you, you're already running! You can get out of that plume with enough time to take a sip of water. This same tactic can be applied to landslides (just be careful you don't run into a landslide NOT targeted at you!)
The last bit of information I have to share with you all still struggling with titan is similar to what others have told you; LEARN* THE FIGHT. Now, you may have noticed that little asterisk. That's because, for those of you who DON'T know the fight, we're going to cheat. At the end of this this thread, I'll post titan's rotations. WRITE THEM DOWN, and put the sheet of paper in a visible spot next to your monitor. Next time you're doing titan, reference this next time you don't know what's going to happen next (just don't stare at it for longer than a second; quick glances!). I used a cheat sheet back when I didn't know titan's rotations and it helped IMMENSELY.
Well, that's all I have to say; titan's rotations below. Remember, don't look like an idiot who eats every plume. Stop blaming lag, and learn* the fight.
PHASE 1
Landslide -> Stomp |-> Jump
PHASE 2
Plumes -> Landslide -> Stomp |-> Jump
PHASE 3
Landslide -> Plumes -> Bombs -> Landslide -> Plumes -> Jail -> Stomp |-> Jump
PHASE 4
Jail -> Landslide -> Plumes -> Stomp -> Jail(IGNORE) -> Landslide -> Plumes -> Pass/Fail
PHASE 5
Mountain Buster -> Stomp -> Plumes -> Bombs & Landslide -> Mountain Buster -> Plumes -> Jail -> Landslide |