There is one statement that in Japanese called the 3 Admirals the "Strongest fighting power of the WG"
The GK's are referred to as the strongest unit in this magazine. But unit also means a sub-division or section. So therefore if we took this magazine the GK's are the strongest Sub-Division of the WG.
But the Admirals aren't a Unit. Admiral is a Rank, They are individuals that command independently at different locations etc. "Most powerful officers"
But the God Knights are more of an elite cohesive unit, that complete missions in groups. And the 3 admirals for example have never been referred to as a unit anyway, sharing the same rank doesn't mean this. They aren't a fixed group like God's knights. Even if they can all be deployed at the same, it wouldn't change this.
That would just be sending 3 of the strongest martial pillars of the WG to do the same task. So the Admirals represent the strongest fighting force.
Whereas the GK's are the strongest within the category of organised units, like CP0 for example.
But even then it's not impossible that the group leeching off Imu's power and immortality could come to eclipse the Admirals depending on Imu's will.
However, if the GK's are weaker it's still not impossible they could beat the 3 admirals through leeching off Imu's regeneration medicine in a battle of attrition and hax.
Though some of you might then say if they can beat them they are stronger end of. But a weaker group with enough prep time and time in general, could beat a stronger fighting force.
They are Knights of God, and therefore when you fight a God's knight, you're not just fighting the Knight, you're fighting "god/Imu" as well. Because Imu is giving them power, and can take over their will as well as possess them at any time he wishes. They are his pieces on the chess board.