I still say that ganondorf took on the guise of Aghanim to fool the king, since he was known in his original form. he became an advisor and then betrayed him, using his power to possess the guards and capture the girls to open the DW and allow ganon to escape; possibly he could not bring the ToP with him, and therefore can only return in his gerudo form. his armies, triforce power, and his Ganon form were still sealed away and could not take over the LW until he destroys the seal.
Well for the record, Twinrova refers to Ganon as the Daimaou about a dozen times in OoX.
When they resurrect him, he gives himself the title of Yami no Maou...just one of the reasons that I like OoT-WW-PH-LoZ-AoL-OoX as a segment prior to FSA-aLttP...lumps all the Daimaou game together, and all the games of Yami no Maou together. OoX then serves as the connector game, as he's referenced as having been the Daimaou when he was alive, but calls himself the Yami no Maou when he's resurrected.
it has nothing to do with the amount of power. It is just a change in name.
Even if we were to be enslaved in the galaxy's cycle of rebirth, the feelings that were left behind will open the door! Even if the infinite universe were to go against us, our burning blood will cut through fate! We'll break through heavens and dimensions! We'll show you our path through force! WHO THE HELL DO YOU THINK WE ARE!?