Everyone knows who the Elders are, everyone knows who the HK are. The HK are confirmed to be their own military faction within the WG.
Then we have this panel about the Admirals being the strongest fighting power in the WG.
The fact that there is even a debate is ridiculous.
To be honest, Oda can easily bypass this statement due to this
The Marines are considered as the "public" face of the world government, which implies that other forces(HKs, Gorosei, etc) aren't considered in the balance of power
And it makes sense considering the HKs, Gorosei and Co stay in the Holy Land, when the Marines operate in all the seas from East blue to the new world
With that said, from what we know of the HKs, only Shamrock should potentially be a top tier(outside of Garling who became a Gorosei), so in terms of power lvl, discounting immortality, the Admirals as a whole should still be superior to the HKs