I hope he lets her taste defeat at least by a bit and makes it look like she got distracted or something, either way the intent is to fail him so he might as well beat her
I say he should probably just go with it, saving the world literally means uniting the will of everyone..
the Goddess never said save mankind/humans only so it's fair game
i honestly feel bad for the guy, he probably never had the courage to talk to them normally again so he decided on his own that they changed and only they were the ones who changed not realizing that maybe he did too