If the Necromancer Tower won, the Hero Academy was going to get rid of their enemies, the Demon Sect, without even having to move a single finger.
If the Necromancer Tower was destroyed, it was still going to leave the other two forces extremely weak. At that point, the Hero Continent could destroy them, conquering the four continents.
The Hero Academy had the motives, as well as the ability to achieve something like this.
'Finally you are doing something useful.'
Even though Anya was not a good person, Eren still complimented her in his mind. She was muddling the waters, which tossed the blame at the Hero Academy.
If the Necromancer Tower war could drag even the Hero Academy into this mess, then it was even better. Even though he didn't need any blood of the Southern Overlord, it was still good to have the Southern Continent weakened.