I suggest maybe re-reading the story with an open mind and dabbling a bit in the novels, subtext is just as important as any other key aspect of the narrative. Personally, in my experience as a queer woman who is the same age as the protagonists, shit happens. Real life isn't pg-13.
i also think such a storyline is a bit problematic, but in my opinion, reducing such a complex dynamic to "sisterly" affection is a reach. When we consider Sorawo's entire family arc and the fact that Satsuki basically groomed highschoolers for fun, it's clear that Urasekai Picnic uses subjectivity and nuance as a way to explore complex issues. If you tried hard enough, you could even say that Sorawo and Toriko's story is strictly platonic solely on the basis that nothing is said out loud or explicitly.
Some people just don't care to explore nuanced, morally ambiguous dynamics and that's fine, but you could be potentially missing a core part of the story here.