Latency is a real issue. I'm worried about endgame for that reason above all others. The worst isn't just lag but a clear discrepancy between clients. Put it simply, it means "not equal chances" between players, "shorter" timings / windows of opportunity for some players.
I'm an EU player on an EU-flagged server. Yet I keep observing higher latency on my client than NA players'. On Ifrit HM for instance, I have about 0.5 seconds to stun Eruptions (when the bar appears it's already halfway through...), which makes it very stressful and sometimes even impossible, considering you have to refrain from interrupting the other cast (thus read the name of the spell, and by the time you've done that...). More frustrating is when I see the stun being performed by my character but the bar still moves for half a second or so (after the shield hit!), and that bar sometimes even finishes, though I did stun before that.
I've confirmed this on Garuda yesterday, I was seeing myself hidden behind a rock and another player hiding AFTER me, but he saw the exact opposite: I was after him on his client... :confused: in the end I got hit, he didn't. How so??!
Also, some NA players are verbally abusing others for being "unable to play correctly" when we clearly don't share the same experience (note that I don't blame them for SE's shortcoming but for their lack of understanding).
I think our characters are client-side while mobs are server-side, and it's quite frustrating to account for that. AoE indications on the ground may not always be reliably used, if I don't have some margin of error I end up being caught in an AoE even though I was clearly outside (Titan, etc.) That's a weird and sub-par design for endgame PvE.
