UK player here - London
I've played FF14 on two different ISP's now, Virgin and Plusnet ( three if you count 1.0 ), Can't say i have any of the issues people complain about. I get lag spikes like everyone else, very few and far between though. The mechanics of some fights are such that there is no room for error, you see the thing on the ground, you start movin immediately or else you're going to get hit.
I feel for the players who have the problems described, but when the majority of players don't have them, SE has to come to the conclusion that the problem is not at their end but the other side, whether it be ISP or PC related
Personally what i think is happening to the majority of people complaining about this is the ff14 traffic being flagged as P2P and being traffic shaped and Qos'd to hell, a lot of ISP's do this and don't tell end customers.
Heck I've played tethered via phone ( 3g not even 4G ) and its been ok, barring some dc's