Thats not the argument though the argument is 1 Admiral vs one of the 4 Emperors.

Its pretty clear that if 2 Emperors showed up at Marineford there they probably would of lost. Now imagine if 3 showed up.

The entire Navy force which includes all 3 Admirals plus the 7 warlords is there to counter the 4 Emperors as separate and not working together. Thats the balance. So if 2 or 3 of the Emperors start working together that balance would be destroyed. So you can assume that 1 Emperor > 1 Admiral. Otherwise they wouldn't be worried if 1 or 2 emperors decide to work together. Since they have 3 Admirals right? And their Navy force is larger than the Emperors.