I totally agree with you.

I play a white mage, and of course casting a lot during dongeons.
I'm experiencing 1-2 seconds every 5 seconds quite often.
Avoiding AOE is problematic, and sometimes due to the lag, i see the tank pass from 100% HP to 5% after the lag without having the time to react.

Yesterday I had a 15 seconds lag. I was casting cure spells, the animations were visible, but no result on HP was visible, all other players seem frozen.
And when i got out of the lag (15sec later), 2 players were dead, and the other far away fleeing.

Passing Titan fight was a real nightmare.

So please Yoshida SAN, please do something, and place the EU servers in Europe and not in america.

Globally the content is really great, but these dongeons should be the best part of the game, and it turns into a nightmare because of this lag issue.