Personally I think the two tracks sound nothing like each other - the two don't sound similar in terms of actual leitmotif other than they use similar instruments. Also just because FFXIV 1.0 came out after Nier, doesn't mean the music was composed at the same time - Uematsu actually composed FFXIV 1.0's OST under contract at his own studio independently from SE, and had already finished most, if not all, of the OST by the time the game went up for Alpha and Beta testing earlier in 2010, around the time Nier was released (most likely he had already finished most of it by 2009). So it's highly unlikely he deliberately set out to plagiarize Nier's OST.