Which is exactly my point. They were arguing that Cass tricked Priscilla into poisoning to take control then threw her away when she wasn't needed. There is literally no evidence of this. From what we're provided in came Cass's mother side wanted to start the coup and poison the king anyway since they believe he killed Cass's mother. Their argument is literally that Cass admitted to lying to a different character, so everything that comes out of the character's mouth must be a lie and she's manipulating everyone all the time.
The screenshot they provided is Elin accusing Cass of wanting to sow chaos. Again no evidence that Cass herself started the fire, and it's just speculation made by another character..
And another quote saying that cass killed some random guy is evidence that Cass tricked priscilla, which is completely unrelated.
After that their only other screenshot is a dream vision which are all supposed to be vague and could even be argued that Cass would EVENTUALLY lose her mind rather than being insane from the start like he's arguing. So he's didn't provide any evidence. He's just shitting on a character he dislikes. I've got no problem with it, but even in your own comment you pointed out the issues with his argument. Screen shots and quotes are completely useless when taken out of context. None of them are evidence.
Also one of his quotes is literally just the mc talking to a vampire. Cass hasn't even met that character so I don't even know why that one was included
Aight, one last message from me on the matter. I'm not going to say anything on what they said or what you said instead I'll simply lay down facts from what I've encountered in game.
Cass did not trick Priscilla at all, she was simply aware of her intent to poison the king. Priscilla's side was also from what I understand unaware of her intentions, it was something she decided to do for herself, they never intended to start a Coup or cause any form of damage to the Empire. She also didn't intend to start a Coup or to damage the Empire, she just wanted to get rid of the person she believed killed her sister. Let's not forget that they weren't in a position to do anything to the Empire at the time since they themselves were on the verge of a Rebellion/Civil War.
Onto the idea of Cass setting fire to the capital, one of two things happened here. Either one she gave the order or two she's incompetent and can't control her own men, there's no room to argue this or to try to weasel out of it at least not with what we currently have. Any other cause for it is either incredibly unlikely or we have no evidence to support.
For the final point being Cass's mental state. She is utterly insane, this isn't up for debate she simply is, the game acknowledges that she is.
More evidence for her lack of sanity or rather mental instability is just how prone to violence she is, let's not forget that she slashed the MC's face when they were kids over an argument that really hadn't escalated to that point yet. She's also fully willing to kill anyone who get's in her path and has absolutely no qualms with murdering innocents if she needs to.
Anyway, this is my final message on the matter, if you don't agree at this point your clearly not going to no matter what anyone say's or gives you as evidence. Any further debate on the matter is pointless.