We know that in the twisted mindset of Green Bull, a mindset that fears Kaido and runs away from Shanks and performs fraudulent feats against exhausted and injured opponents, the admirals of the Marine headquarters cannot afford to lose to "subordinates", but it is acceptable for them to lose to captains.
Aokiji being declared as a subordinate means that Green Bull doesn't see himself losing to him? Which means that we can assume that according to Green Bull's twisted mindset, he is more powerful than Aokiji, who is equal to Akainu and almost killed him in a 10-day fight, imagine Shanks and Kaido, who put fear in Green Bull, who according to his own words cannot afford to lose to Aokiji, a subordinate.