It's probably a temporary trend to see numbers that low due to FFXIV's very successful relaunch recently. On Quetz 3-4 weeks ago normal NA prime time was around 1.2k easy, now it's sitting around 500. Weekends creep back up to 1.2k still when NA and JP schedules overlap.

It's typical when a major title with crossover appeal comes out that XI numbers drop, I recall this happening with Diabolos 3 and Skyrim, though not quite as drastic, probably since XIV has the post potential crossover appeal to XI fans. I think you'll see total players climb back up a good bit after the XIV free trial is over and the next XI version update is released.