Now, look, we can argue about if Xebex came off cooler, or Imu did. But I think we can all agree on one thing.
The Holy Knights SUCK at their jobs. Literally, can they protect *anyone*?
1. I think, based on Ginny getting kidnapped, the God's Knights actually do stuff outside Marijoa most of the time. Unlike the Gorosei, the God's Knights are teleporting around everywhere.
2. The God's Knights serve/protect Imu. They aren't Gods' Knights, as in the Knights of the Celestial Dragons, they're God's Knights, Imu's personal security detail. IE, they don't give much of a shit if Charlos gets smacked by Myosgard; none of their business, their job is to defend Imu, and pursue Imu's interests, PERIOD.
The Admirals/Marines are supposed to protect the Celestial Dragons, hence Akainu showing up to deliver red hot lobster.
The God's Knights are Imu's personal strike unit.