It's been proven that people can play the game without issue as far as Autralia.
Adding in a European Datacentre would NOT fix the issues you're describing.
Square Enix cannot compensate for the route your ISP and particular connection will take from You > Server > You > Server (etc).
Each 'hop' has the potential to cause issues for you.
The vast majority of the times where people have issues they find the issue lies with their connection, their area or the particular route it's taking to travel to and from the data centre.
Adding in another hundred-thousand dollar(s) facility is not something they're currently willing to do as it's a huge financial investment.
You'd be surprised, that the majority of the time this comes up, simply boils down to people not knowing the fight, watching the graphics as opposed to the cast-bar (cast-bar ending time is the TRUE hit, not the in-game graphic).
And in some cases people genuinely do lag, and it's almost always their connection. As someone who's played in Ireland & England and plays frequently with players from the Middle East, Asia and Australia who have with complete easy beaten all the content the game has to offer, it's safe to say it's not a "I live in [X]" issue.
Not everyone has a great connection, not everyone's internet traffic is going to get routed along the fastest route. The area you live in may suffer from internet traffic congestion at particular times of the day, or is it limtied by your ISP for certain types of traffic.
Basically, slapping in a new EU datacentre wouldn't fix the big issues, if they did this they'd have to add in at least 2-3 more localized datacentres to "Be Fair" for various wordly regions, but the cost would justify the small number of people that actually suffer from this.
TL;DR
It's most likely YOUR connection between You > Server.
Servers are Expensive, they won't be opening a new data centre anytime soon.
Unless EVERYONE/Vast Majoity is having the issue, it's not a big problem. (Which currently is a tiny minority)