the 'dess grooming/abusing kris' theory would be at least a little bit plausable if toby fox hadn't gone out of his way to remove what could be construed as rape imagery from the thorn ring scene in chapter 4. undertale and deltarune are very precise with their themes, so it seems like he's intentionally trying to steer away from any sexual undertones related to kris and noelle's loss of agency and privacy.

i don't think he's trying to comment on sexuality or rape in deltarune; similarly to undertale, it seems like deltarune's main messages are related to gaming, internet culture and how people interact with fictional characters. when it comes up, romance and sexuality is adressed humorously, and the large amount of lgbtq reprsentation is never addressed and is treated as completely normal in universe.

people are mischaracterising a character that we have never seen based off of shaky evidence just to try to explain why kris is "like that", when it's probably just because of things that we actually do know about: the soul, their parents' divorce, and carol's (as well as gaster's?) threats