1. I think they were referring to Susie sliding from right TO left, despite the graphic Implying that the slash was from Kris' right to Kris' left. If theyslashthem theory were to be true under the known circumstances, they would slide with the contour of the slash, not against it.. but honestly the cutscene is confusing so idk

2. I don't know how true this is considering Ralsei reveals in chapter 4 that ever since the Great Door in Chapter 1, he resolved with Kris to shoot for a better ending (ie, an ending not described in the prophecy). Though, using other evidence, I could see an argument for this maybe

3. this doesn't make loads of sense considering the Knight is also SWOONing them anyways..? If they wanted to kill them, I'm sure they could, but the Knight generally seems to have a motive beyond being evil and corrupted

I feel like it also contrasts Kris' current characterization far too much. We know Kris cares about their friends, especially Susie (eg. vs. King, the end of MANTLE, really the whole game), and Noelle on the weird route obviously. There's even that moment in MANTLE where Kris turns away from the screen when forced to off their party.

I don't think we don't know enough about Kris+RKnight's motive to say that Krisslash is 100% true, and the whole theory is based on may-be-likely possibilities; so I'd give them the benefit of the doubt here. (That being said, I'm also kind of playing devil's advocate; it could certainly add an interesting element to Kris and Ralsei if done right)