>>712853045
One problem Chapter 4's writing does have is how much it hinges on the player having found an optional boss fight.
It makes sense if you do find it. But if you don't?

>Susie basically chases around a strange figure that looks nothing like Gerson, weirdly convinced it is Gerson despite never having seen him with his armour on
>Starts pretending this character fighting her totally has to be him, despite previously believing Gerson is too old and frail to fight and would supposedly still believe that if she never had his optional boss fight
>Green soul gimmick's return comes out of nowhere because you missed the fight properly re-introducing it, feels awkward, though the fight is still cool
>The creepy reveal it isn't Gerson fall flat, because again, without having seen him with his armour, it didn't look like him to begin with

And yeah the thing you say is a Deus Ex Machina ends up feeling a bit like one mainly because Gerson actually being a strong fighter was never established without his boss fight.