OH YEAH, I FORGOT
If you choose to go with the idea that Sonic's counterpart is also King Arthur (the hedgehog, not illusion), then you could also draw up reasons for why he isn't the king in the game.
Mordred was prophesied to kill Arthur, so (as a baby), Mordred was sent on a ship that was supposed to be destroyed, killing everyone aboard it. However, Mordred survived and eventually made his way to Camelot, becoming a knight and usurping Arthur's throne temporarily.
For a parallel, perhaps the illusion Arthur's fate was to be killed by Arthur the hedgehog (and rightful king). In an attempt to escape his fate, he asked for all the hedgehog children to be sent on a boat that was supposed to crash, killing everyone on board, but Arthur ended up surviving, and once Sonic left, took the throne.
If there’s one thing I love in SatBK, it’s that DESPITE being crowned as King Arthur, he actually fills 2 roles (Arthur and Mordred).
Him filling Arthur’s role is PRETTY self explanatory. He’s crowned king at the end of the game, pulled the sword from the stone, leads the knights and kingdom, etc. But Mordred’s role is something ENTIRELY different.
First, Mordred and Sonic both doomed Camelot in different ways: Mordred with usurping Arthur and taking his throne, Sonic with giving the scabbard to Merlina resulted in the kingdom almost being destroyed. Mordred disregarded the code of Chivalry (Sonic does this out of overall disinterest and his morals, Mordred has more lustful habits and unchivalrous behaviors, which Sonic DOES NOT have).
Then, we have the more obvious parallels between them. Mordred killed Arthur, and Sonic did the same with the illusionary Arthur. Mordred used Clarent to kill him, a sword that Arthur used in ceremonies, and BEFORE getting Caliburn, the sword Sonic uses for Misty Lake’s tutorial levels is, in fact, Clarent as well.
This is all REALLY circumstantial, and of course it’s not 100% accurate, I just thought it was a really cool thing to mention.
But I also really want to know what this would mean for Merlina’s dialogue now. After all: “Arthur is struck down by his son Mordred, and departs for Avalon”, but if Sonic fills the roles of BOTH Arthur and Mordred, then Camelot’s ending plays out much differently.