It's a little weird to me that Sleipnir barely did anything in this fight despite being a mythical beast. I wonder if the goal was just to introduce the concept of a flying horse so that it can be used later on? In the legends, Gawain owns a warhorse called Gringolet that was apparently very skilled in battle. Normal horses can't survive the kind of fights this series has, but perhaps a particularly powerful mythical steed just might be able to pull it off? From nigh impossible to neigh impossible. If it turns out that Gawain is the last of the Knights of the Apocalypse, a flying horse would enable him to fly like the other KOA. Percy has his cape, Tristan has the potential to form wings and Lance can always learn to levitate like Elaine, but Gawain would need something more than just Sunshine to take to the skies. This would also fit nicely with the idea of the last KOA being a half-giant half-human, because Sleipnir was a little too big for a normal human to comfortably ride it, but simultaneously a little too small for an actual giant.
I am inferring things, so I could be wrong, but it does seem like much more happen then where we left off. Yeah, we were told that by Donny the story of what happen with Camelot, which was then counter by Tristan stating it did still exist. Given the knowledge he has shown so far, it seems like Tristan would know what he's talking about and what the general public like Donny knows is false. While the timeline could be due to a mistake, it could also be when the event that changed Arthur happen. That would fit with what we know regarding the schism with his knights that caused some of them to flee/cut ties. I guess Ardbeg's flashback could have happen before sixteen years ago, but that would suggest that there were demons running around destroying things some time after that war ended, since Arthur was unconscious til Merlin made him into a vessel for Chaos. It seems unlikely there was widespread demon attacks like that. And I haven't seen the film, so I don't know what happens in it, but I presume that Arthur wasn't shown as opposing the other races, which was a specific point of Arthur's offer to Ardbeg.
When Lancelot said that Camelot still exists, he also said "you can't get there by normal means", which suggests that he was talking about the weird castle floating in space that appeared in that same chapter. Donny's not wrong, it's just that the general public only knows about the physical Camelot which indeed no longer exists. He does mention that Arthur is said to be in hiding, but normal people have no way of knowing about the existence of some kind of a separate dimension. The destruction of Camelot that Donny is referring to was the Demon King wiping out the kingdom, and that timeline also fits with some demons attacking Ardbeg's village. There's no way that incident happened 2 years after the DK's defeat because Ardbeg is specifically talking about the holy war when that scene is first shown. Also, didn't Arthur's revival happen right after the DK's death? As soon as the skies cleared after the destruction of the Commandments, Bartra declared that there would be a celebration that day. The Chaos stuff happened when Merlin teleported the Sins away during that party. Cath was dealt with by evening and Arthur met Nanashi in Camelot at night, presumably right after that.
The way I see it, when you account for Donny's words about Camelot and Ardbeg's encounter with Arthur, the only explanation that fits is that Arthur turned evil pretty much right after obtaining his powers. It would take some days or weeks for everyone to learn about the end of the holy war, which resulted in some random demons attacking Ardbeg's village even though their king was already dead. It doesn't really make sense for there to have been some separate event that made Arthur become evil, because what could possibly be worse than the demons almost killing him and then wiping out his kingdom? Furthermore, I don't think Arthur became evil because of some sort of an incident with the other clans to begin with. Remember that he doesn't just want the other clans gone now, he's also started torturing his own subordinates. That's completely out of character for him and there's no reason why a bad experience with the non-human clans would make him behave like this towards his fellow humans. There's got to be some other explanation. When Arthur started torturing Ironside, his eyes suddenly turned black, which also happened when he first obtained his Chaos powers and attacked Meliodas in a rage. I think a loss of control is the actual reason behind Arthur turning evil, not some kind of a dispute that soured his opinion of the other clans.
As for the movie, the only real scene with Arthur involves him placing rocks as grave markers in the ruins of Camelot. He gives a speech while crying just as he is interrupted by some mind controlled fairies and giants. In a brief post-credits scene Arthur is still standing in that same spot and we see a couple of skulls, which I think is meant to imply that he killed them. No idea why there weren't any other remains though.
