Yeah, Rem's character arc is that of a cannonball fired off a cliff. I know others didn't like the forest section but I actually think that was some of her most interesting stuff, with the up front rage and self-loathing, the look into her survivor's guilt and the pressure she'd been putting herself under.

After that she stops being a character I care about. Not because she's happy (I like happy characters!). Not even necessarily because she loses agency (she can choose to be the perfect waifu for Subaru, same as post-feminism women can choose to be homemakers if they want to).

I stopped caring about her because she became boring. Characters need a conflict, and once Subaru wakes up after the forest she no longer has one. There's no longer any competing motivations going on so every single one of her actions can be predicted in advance.

She'd be interesting again if she decided to fight for Subaru's love; if she was torn between her desire for him to be by her side and her desire for him to be happy. That's a good subplot for a story. But she's not torn, because she's given up and isn't interested in doing anything more for herself.

That said, if you accept that Rem is now just a plot device and that Subaru is the only actual character in the show, I think plotdevice!Rem worked well in this episode for giving Subaru the push he needed to get started on his redemption. That's where I started from with my original comment.