Just throwing this out there as a suggestion....

I had trouble the first couple times dodging plumes in Titan HM, and I could definitely notice a lag. I then port-forwarded my router (properly, not using portforward.com), and added exclusions to my firewall for FFXIV. I also updated to the latest video card drivers. The difference in the first fight after doing this was night and day.

I'll be the first to admit that SE's servers are absolute garbage, but if you haven't done ALL of the stuff I mentioned in an attempt to fix your lag issue, then it's still your fault that you're lagging. If you have, well, start stalking SE's customer service lines until they get frustrated and fix it.