I've been having the same issues with rubber-banding characters and attacks hitting long after I had moved out of the area and I did some investigation to the NA datacenter. This occurs primarily in instanced dungeons and is much worse during the evenings. During off times such as weekday mornings it is much less noticeable or fight-wrecking. What I found is it is clearly not on my ISP, it is on the Montreal end, in between the datacenter and the iweb cloud server where bad packet loss is happening. Square Enix, if you're contracted with this "iweb" service, they are not doing a good job lately. Here is my pathping and you can see 4% packet loss, all in that area.

Computing statistics for 325 seconds...
Source to Here This Node/Link
Hop RTT Lost/Sent = Pct Lost/Sent = Pct Address
0 [192.168.0.2] 0/ 100 = 0% |
1 0ms 0/ 100 = 0% 0/ 100 = 0% qwestmodem.Home [192.168.0.1] 0/ 100 = 0% |
2 24ms 0/ 100 = 0% 0/ 100 = 0% hlrn-dsl-gw06.hlrn.qwest.net [207.225.112.6] 0/ 100 = 0% |
3 21ms 0/ 100 = 0% 0/ 100 = 0% hlrn-agw1.inet.qwest.net [71.217.188.41] 0/ 100 = 0% |
4 54ms 0/ 100 = 0% 0/ 100 = 0% los-brdr-01.inet.qwest.net [67.14.102.30] 0/ 100 = 0% |
5 57ms 0/ 100 = 0% 0/ 100 = 0% 63.146.26.146 0/ 100 = 0% |
6 54ms 0/ 100 = 0% 0/ 100 = 0% if-3-2.tcore1.PDI-Palo-Alto.as6453.net [66.198.127.25] 0/ 100 = 0% |
7 56ms 0/ 100 = 0% 0/ 100 = 0% if-2-2.tcore2.PDI-Palo-Alto.as6453.net [66.198.127.2] 0/ 100 = 0% |
8 73ms 0/ 100 = 0% 0/ 100 = 0% if-11-3.tcore2.CT8-Chicago.as6453.net [66.198.144.58] 0/ 100 = 0% |
9 115ms 0/ 100 = 0% 0/ 100 = 0% if-3-2.tcore1.W6C-Montreal.as6453.net [66.198.96.45] 0/ 100 = 0% |
10 --- 100/ 100 =100% 100/ 100 =100% 66.198.96.58 0/ 100 = 0% |
11 --- 100/ 100 =100% 100/ 100 =100% te7-3.dr9.mtl.iweb.com [67.205.127.214] 0/ 100 = 0% |
12 113ms 4/ 100 = 4% 4/ 100 = 4% 72.55.128.44 0/ 100 = 0% |
13 113ms 0/ 100 = 0% 0/ 100 = 0% 184.107.107.176

Trace complete.

I really hope you can get things sorted before the expansion. The game was so much fun, and had smooth dungeons for me just a month ago but now it's become a tragic mess.