We recently learned through the demon village that even the monstrous demons have free will and their own personalities. Some individuals are more evil than others, just like with humans and the other clans. That alone is enough to explain why some demons would continue fighting even after they were no longer being ordered to.
True, though as mentioned, given how the demons have been retconned since their first appearance, that would be surprising. After all, they were made the unfortunate victims of the Holy Wars, fighting for survival or under the control of others.
Lancelot did indeed correct Donny, but only to point out that the kingdom still exists. He didn't disagree regarding how and when Camelot was destroyed. I don't think Donny is wrong about the survivors, I mean he specifically says that "They say the king went into hiding, with his few surviving knights and countrymen." We know that a whole bunch of them died because Arthur built a massive graveyard in the ruins of the kingdom. These two accounts don't even contradict each other, because Arthur going into hiding after Camelot's destruction fits perfectly with Lancelot mentioning that Camelot cannot be accessed through normal means. I'd wager the reason behind Arthur wanting to hide the kingdom is connected with his overall shift in personality that seemed to have happened almost immediately after he obtained his Chaos powers if Ardbeg's story is to be believed.
Well I said he was wrong because according to Merlin in the previous series, most of the citizens of Camelot were saved. And apparently even some of those that had been hidden were shown surviving. So if Arthur fled at the end of the previous series, it wouldn't have been with just a few, unless a majority decided to remain in Liones. The story as told is quite different from what we know the reality of the situation was. There's also the implication that the demons were believed to have left sixteen years ago, but there apparently being more to it then that to the point that the sealing of them would be serious trouble, though perhaps that is solely based on Meliodas and his strength.
Camelot wasn't just said to have been destroyed by a demon, but specifically by the leader of the demons. It would take some serious plot developments for that to refer to Meliodas. Calling a conflict between Camelot and Liones a holy war because the Sins are from different clans is a bit of a stretch. That same logic could be used to label an event like the Sins' attacking Liones a holy war as well. In order for Donny's words to refer to a war between Camelot and Liones, Nakaba would have to be deliberately misleading the audience by making claims that are only true on a vague technicality. This would not just be complicated, but downright convoluted. It would also negatively affect the story of NNT. Major events like the holy war or the destruction of Camelot would become much less impactful if it turned out the same things happened again a mere two years later. It's a very drastic course of action to explain away a minor discrepancy in the dates. I am aware that Nakaba has mentioned the timeline of 16 years multiple times, but consider that Anne in chapter 24 says "the Seven Deadly Sins defeated the king of the demon race in the holy war". Hearing her say that would surely confuse Donny if his version of the story was that Meliodas was the demon king in the holy war. It would also be a weird move for Nakaba to not differentiate between the two wars in any way for the sake of the audience, in fact every character keeps referring to 'the' holy war as if they only know of one.
Not really, if it's propaganda. We already had characters like Ironside publicly calling Liones evil and acting as if they're saving people from it. And it's not that much of a stretch considering the difference between this potential Holy War and the second Holy War is three goddesses. Them and the Sins were the only non-humans involved, so the overall argument would be the same. It's not complicated if it's suppose to be a twist. We've already been given several hints that the two are already in conflict and are currently attempting to gain an edge, having it be that they had previous clashed wouldn't be that convoluted and would lead to an explanation on why they're both gathering the means as they are. And I would say the previous series would still be affected negatively going from Arthur and the Sins being allies to them randomly being enemies without any triggering event. Additionally, assuming that the second Holy War is the trigger behind the way Arthur and his knights are acting would only make sense if they were just against the demons, but as we have seen, they're also against the giants and fairies, meaning something had to have cause them to become enemies.
The conclusion that makes the most sense to me is that Nakaba simply screwed up the timeline. That way Donny, Anne, Nasiens, Arthur and Ardbeg's comments about the holy war all match. The demons wiped out Camelot and destroyed villages during the holy war until the Sins defeated their king, after which the demons left Britannia and Arthur went into hiding. Nakaba being confused about the timeline wouldn't surprise me in the slightest, since the fans were also very confused about it initially. When Nakaba said in an early Q&A that the sequel takes place 16 years after NNT, we didn't understand whether that meant 16 years after the Demon King's defeat, 16 years after Tristan and Lancelot were born or 16 years after Tristan's 10th birthday. I can't remember if that was ever clarified either. It seems like Nakaba went with the second option, but keeps referring to the holy war as if he had picked the first option. I think he just messed up, or maybe we've misunderstood something and Tristan and Lancelot are actually only 14.5-15 years old right now.
I would assume that if there was an error with the timeline, that would have been corrected after the first time. Or not even mentioned, since we would already be aware when said Holy War took place. That we have it being repeated multiple times would suggest that it was on purpose, or an error made canon. Wasn't aware of that confusion with Nakaba's comment.
