Are you previewing the output on an NTSC monitor? As my own rule, I use the animation settings for output in AE. When brought in to FCP, the movie looks very grainy. (same goes for all text in FCP–it looks like garbage unless viewed on an external monitor) If you are monitoring the output on an NTSC monitor, you should find completely different results. If you do not have an monitor, export the timeline to a movie and burn it to a DVD and check yourself.
Hope this helps
Tim