So, the God's Knights are not necessarily comprised of Celestial Dragons by birth.
I wonder if it's like half-and-half CDs and people brought in to serve them.
Imu is very protective of CDs. It would make sense for the Holy Knights to recruit and use non-Celestial Dragons as the primary force.
This is why we only see Gunko attacking; she's subservient to Pranks, and disposable compared to him.
Also possible that so many Holy Knights died in "God Valley" (IE, the Celestial Dragons, the "God", were killed an let down in a "valley", as valleys are often associated with death) that they had to recruit from outside forces.