I feel like whatsherface knight girl is accepting it all a bit too easily? Instantly agreeing with the demon lord last chapter instead of sticking to "no the mind control magic was totally you" is one thing but this chapter it's practically collapsing the entire religious (& to a lesser extend historical) part of her worldview and she's just like "damn that's wild". Mirio at least has the excuse of having interacted with the demon lord and love/horny.
I mean when she first thought the 'hero' was actually a sociopathic scum of a human who enslaved the demon lord, would
you question what God was thinking having picked such a person as the hero? Though small, that's probably the first time she doubted God's judgement, and if faith has some play in their powers of influence, then that hold may grow weaker the more holes she finds in God's judgement as she observed Mirio and Ivelle.
Now using the hero, who was probably at most a decent person from the start, as a vessel for God to not only enact revenge but also break down the demon lord into total submission before eliminating her completely and getting a kick out of it in the process?
That seems more likely for why the hero's behavior seems so far different than it was originally.