My biggest evidence for Dess being the knight is that anything else would just be lame and underwhelming. in my opinion
Our other biggest candidates are a middle-aged politician and some sick guy-- and imagining Rudy shambling out of his hospital bed just to turn Tenna into a past-tense before aurafarming on the fun gang is moreso lowkey hilarious than climactic.
Yeah, Carol has the katana or whatever, she COULD be the knight! It's entirely possible that she briskly jogged her merry way through hometown after scolding Noelle and made it to the church in time to make the ch4 dark fountain. yeah, I could buy it.
Sure! Rudy COULD be faking his sickness. but would that REALLY be satisfying or interesting at all?
there's plenty of other evidence for dess knight, but sometimes "it makes sense and is cool" is a compelling argument
oh yeah and papyrus is there too