All depends on the definition of completion.
By getting the platinum trophy, plenty have. Not THAT hard to get.
If by completing the 2.0 arc (Completed all dungeons, trials, raid stories, all of binding coil), your character is maxed with jobs, and you're waiting for the final part of the story, some have. Those who have "saved the realm from the elder primal bahamut" are few, but they have "completed FFXIV" for now.
If completion means completing all craft logs, gathering logs, all achievements, all extra side stuff, gotten all obtainable items the game has to offer....:0% have completed the game. Why? Because it's virtually impossible to complete ALL of that. If by some miracle someone has, that person needs a life more than any other person.
