I understood what he meant pretty well, and I don't think he's wrong. When he says "theme" he means specific melodic themes, like character themes. You're using "theme" in a more generic sense, such as representing a setting, atmosphere, or an idea, and this definition is not applied specifically to music (but can be if the context is explained).
There's absolutely no fault in saying that FFXII's soundtrack was more ambient than FF titles scored by Uematsu. This doesn't make it an inferior soundtrack either; I loved FFXII, I think it's one of the best works by Sakimoto & Co. It's just the difference in writing style. More ambient music is harder to "remember" because clear melodies don't necessarily have to exist to get the music's point across. FFXII does have memorable melodies, but the more atmospheric songs are defined more by instrumentation and progression than by melody as is Uematsu's style.
That being said, I think FFXIV is the most atmospheric collection Uematsu has put together. I'm very pleased with the expected Uematsu classics mixed with a lot of new ideas and inspiration I've heard throughout. Notably, and it almost seems overdone how the first several tracks are bundled together as rock-based battle themes of sorts, I am happy that he has a great production quality on the rock themes. Before "Otherworld" in FFX, I think he kind of avoided jumping into full-on rock because of hardware and production limitations. Now it seems he has a very comfortable set to work with, as well as a very competent audio engineer. And it feels like these several tracks are a result of Uematsu having a lot of fun and freedom in this new digital playground.
I agree with others about the questionable choice of song 15 being the primary battle theme. While this is obviously subject to change, Beneath Bloody Borders (0C) seems to be better-suited because of its neutrality and progression. I think 15 is a great song, though, every time I hear it, I feel as though Zero is going to jump down to Mega Man's rescue and blast the stage into rubble.
I heard Susan Calloway in concert in Chicago, so I immediately recognized her in 1D. I'm not really a big fan of this song. I'd be happy, and not incredibly surprised, if by the final release this gets the full orchestra treatment. The current slow rock ballad with clean guitars and Uematsu's favorite rock organs just don't do it for me.
I also fully expect Twilight Over Thanalan (sp?) (43) to get the full orchestra treatment by the final release. It played very beautifully in Chicago albeit very short. I might think some other things would be combined or this could be lengthened for the orchestra version, but this definitely sounds like a good candidate for his "big theme."
Overall I'm very pleased with this, and a little astonished the soundtrack took such a dramatic change in direction from FFXI. Naoshi Mizuta is a very competent composer; great with atmosphere if not quite as adventurous as his bigger brothers at Square Enix and Uematsu. FFXI was not a very diverse album in terms of dynamics, including Uematsu's contributions, but it's hard to imagine this new music in a game that's similar to FFXI at all. Can't wait to see how it turns out when you're in a zone for hours on end listening to battle themes fade in and fade out.
XI Wiki



