I'd like to add something to the conversation here -

The following is a traceroute to the NA / EU datacenter in Montreal by an ISP in southeastern Europe (Athens, Greece):

Code:
Non-prime time (23:50 BST - 01:50 EET)
Tracing route to 199.91.189.25 over a maximum of 30 hops

  1     1 ms     1 ms     1 ms  dsldevice.lan [192.168.1.1]
  2    25 ms    24 ms    24 ms  bbras-llu-kln-15L500.forthnet.gr [213.16.246.12]

  3    25 ms    24 ms    25 ms  213.16.247.73
  4    28 ms    28 ms    26 ms  core-kln-12Be3.forthnet.gr [213.16.247.17]
  5   25 ms   27 ms   28 ms  te-3-2.car1.Sofia2.Level3.net [212.162.46.109]
  6   65 ms    68 ms    65 ms  4.69.141.109
  7    71 ms    76 ms    73 ms  ae-10-10.ebr3.Frankfurt1.Level3.net [4.69.141.34]
  8    66 ms    66 ms    66 ms  ae-73-73.csw2.Frankfurt1.Level3.net [4.69.163.6]
  9    66 ms    66 ms    65 ms  ae-2-70.edge4.Frankfurt1.Level3.net [4.69.154.72]
 10    77 ms    78 ms    78 ms  4.68.111.146
 11   157 ms   156 ms   157 ms  if-7-2.tcore1.FNM-Frankfurt.as6453.net [195.219.50.2]
 12   156 ms   155 ms   156 ms  if-5-2.tcore1.AV2-Amsterdam.as6453.net [195.219.194.13]
 13   163 ms   160 ms   159 ms  if-2-2.tcore2.AV2-Amsterdam.as6453.net [195.219.194.6]
 14   173 ms   171 ms   172 ms  if-7-2.tcore2.L78-London.as6453.net [80.231.152.14]
 15   158 ms   159 ms   158 ms  if-20-2.tcore2.NYY-NewYork.as6453.net [216.6.99.13]
 16   156 ms   157 ms   155 ms  if-2-2.tcore2.MTT-Montreal.as6453.net [64.86.226.13]
 17   158 ms   158 ms   166 ms  if-0-2.tcore1.MTT-Montreal.as6453.net [216.6.115.89]
 18   159 ms   161 ms   157 ms  if-5-2.tcore1.W6C-Montreal.as6453.net [64.86.31.6]
 19   164 ms   164 ms   163 ms  66.198.96.50
 20   166 ms   166 ms   170 ms  192.34.76.2
 21   182 ms   183 ms   183 ms  199.91.189.234
 22   166 ms   165 ms   165 ms  199.91.189.25

Trace complete.
Code:
Prime time (19:00 BST - 21:00 EET)
 1     1 ms     2 ms     1 ms  192.168.1.1
  2    23 ms    22 ms    22 ms  bbras-llu-kln-15L500.forthnet.gr [213.16.246.12]

  3    23 ms    22 ms    22 ms  213.16.247.73
  4    25 ms    23 ms    23 ms  core-kln-12Be3.forthnet.gr [213.16.247.17]
  5    33 ms    35 ms    33 ms  te-3-2.car1.Sofia2.Level3.net [212.162.46.109]
  6    63 ms    63 ms    62 ms   4.69.141.109
  7    63 ms    67 ms    74 ms  ae-10-10.ebr3.Frankfurt1.Level3.net [4.69.141.34]
  8    64 ms    63 ms    63 ms  ae-93-93.csw4.Frankfurt1.Level3.net [4.69.163.14]
  9    64 ms    63 ms    63 ms  ae-4-90.edge4.Frankfurt1.Level3.net [4.69.154.200]
 10    62 ms    61 ms    62 ms  4.68.111.146
 11   158 ms   158 ms   159 ms  if-4-2.tcore1.PVU-Paris.as6453.net [80.231.153.10]
 12   298 ms   306 ms   319 ms  if-2-2.tcore1.PYE-Paris.as6453.net [80.231.154.18]
 13   332 ms   328 ms   325 ms  if-5-2.tcore1.L78-London.as6453.net [80.231.130.1]
 14   333 ms   316 ms   338 ms  if-1-2.tcore2.L78-London.as6453.net [80.231.130.122]
 15   314 ms   305 ms   303 ms  if-20-2.tcore2.NYY-NewYork.as6453.net [216.6.99.13]
 16   325 ms   328 ms   345 ms  if-5-2.tcore2.MTT-Montreal.as6453.net [216.6.99.30]
 17   332 ms   315 ms   308 ms  if-0-2.tcore1.MTT-Montreal.as6453.net [216.6.115.89]
 18   315 ms   329 ms   342 ms  if-5-2.tcore1.W6C-Montreal.as6453.net [64.86.31.6]
 19   319 ms   324 ms   317 ms  66.198.96.50
 20   336 ms   327 ms   316 ms  192.34.76.2
 21   316 ms   312 ms   305 ms  199.91.189.234
 22   322 ms   318 ms   321 ms  199.91.189.25
Okay. I have submitted these traceroutes to them, via support (and for the first one, which was in the initial ticket, they mercifully said they'd "forward it to the datacenter", something I honestly did not expect, despite being very rational to do so).

I have also told them the following, in an e-mail response:

You will notice that the 300+ ms in Paris or London (in bold above) are over what they should be (Europe-to-Europe connectivity should be at 100 ms or less, as you can see Athens-Frankfurt is "only" 63).

Since after Paris, the rest of the route up to Montreal is entirely within TATA (London, New York, and finally Montreal), I presume that TATA must be the primary / only provider of bandwidth for your Montreal datacenter.

So, it would be wise for Square Enix to take this up with them (TATA). Perhaps they can perform network upgrades or otherwise direct traffic from / to your Montreal datacenter through links which are less congested.


TL;DR: Square Enix / EIDOS Montreal should take up this issue with TATA, to alleviate problems with EU players in general, since the problem is not isolated or restricted to few cases only. It appears that a significant discrepancy exists in "prime time" hours, when links are severely congested and produce double the pings + packet loss, hence normal gameplay under these conditions is totally unfeasible.

Alternatively, Square Enix could decide to deploy some servers in UK, where Square Enix Europe is, and automatically stop worrying about TATA links

Conclusion

I hope you understood the issue from a networking POV, at least as adequately as simple testing can allow this to be done. There are more elaborate ways to test, however, the link congestion will not go away on its own, unless Eidos Montreal decides to significantly change their Internet bandwidth providers and / or take this up with TATA which seems to be the only ones taking EU players to them as things are.