Built-in FFXIV AA is derived from driver.

Normal MSAA uses model edge sampling and 4x MSAA means 2 horizontal, and 2 vertical samples.

FXAA is a SHADER-based AA which gives an incredible performance increase. The down side is, FXAA will looked a little "blurred" compared to normal MSAA and that "Blur" is also what gives the FXAA the "Anti-Aliasing" effect.