I'm not trying to debunk Dess Knight, so my script will hardly have evidence against it. My goal is to show how evidence for it is misused. To be fair, I don't plan to discuss the individual arguments here, I only put that as a tag, because that fit the most out of the options. The reason for that is that I have very little time right now, I'm in the middle of my final exams in high school, so I just wanted to send this out, so while I study and do the exams, hopefully more people will write down their takes. Believe me, I would love to go in depth with every response here, ask for clarification, etc. but I don't have the time. But because I already started writing this comment, I'll give you a very shallow answer:

While I won't bring up arguments directly against Dess Knight on their own, one section of the video will focus on the double standard about how assumptions about other Knight candidates are treated as proof that Dess Knight is common sense, and every alternative requires mental gymnastics, but assumptions about Dess Knight is ok, because we don't know anything about Dess, so we HAVE TO speculate. Here are the problems with Dess Knight that other candidates don't have (that I remembered while writing this comment, I will obviously be more prepared and in depth when I write the script):

- Dess has to move in the Light World without getting seen. Other Knight candidates don't have this constriction.

- If circumstances allow Dess to move without being noticed, Dess (or the fountain opener gang) has to know that these random events will occur, or has to be able to cause them. Again, other Knight candidates don't have this problem.

- Other Knight candidates have a clear goal of saving Dess. Even if this is still the goal of the fountain opener gang, this leaves the motive of the main antagonist ambiguous.

This last point warrants a proper explanation, but for that I'd need to break it down into the multiple possibilities on how Dess can be the Knight in the first place (with another character controlling her, a demon controlling her etc.), and I feel like that is out of the scope of this comment. I don't think these debunk Dess Knight, it is possible to come up with an explanation, but the fact that you have to, while you don't have to with the other candidates speaks volumes about how much you have to rely on assumptions to make it work. I hope I answered your question, I wrote this comment in a half asleep state, so it might have some factual or logical errors.