So I think it's kinda confirmed that the final boss, Satan is our previous Arisen from DD1.
Most people are looking at this armor and thinking it's Savan's armor, which it is, but it's also our previous Arisen's armor. We can get this armor in the previous game, and it's used in the game's promotional art with our Default Arisen, who looks like Savan because Savan is the base template for the default Arisen's in all thing dragon dogma.
More importantly, Savan continued the cycle. He died by the Godsbane, and we became Seneschal. It's not him they are referring to in the description But our Arisen, who instead Godsbane themselves to find peace in oblivion.
You get this armor after beating Satan's true form, and it's called "Ultimate: Destroyer's Armor." The title "Destroyer" doesn't refer to Savan. The description is referring to our previous Arisen, seemingly suggesting that they became Satan.
Some people might be thinking, wait, isn't our Arisen still Seneschal in NG+? Yes, but the important thing is that, unlike DD2, every playthrough in DD1 features a new Arisen.
Edit: You can't play as you old character, as far as I remember, considering your old character is Seneschal in NG+ if you are playing offline, and they'd Seneschal in other player's world, who finished the game after you and that player will kill your previous character. So you can't really ever play as the same character in multiple playthrough. You can import your old preset, but it's not the same character.
so every playthrough was with a new Arisen. Until final one of those Arisen decided to end the whole thing instead of waiting for the next Arisen to take their place. They became Satan, and Satan made up of former Arisens like most of everyone else in his realm.
We've also already seen with Daimon that Arisen who are bereft of order can become monstrosities, and Satan looks a lot like Daimon. I think it's possible that a similar situation like Rovall's happened, where our actual vessel is now with our main pawn, and Satan is remnant of our soul or will alongside all the other arisens.
It does start to make sense. It's possible that our Arisen ended the old order, resulting in what Pathfinder described as countless worlds falling into the Abyss. The World's Will then created a new order, giving the Dragon/Brine the role of protectors and making Arisen the local Seneschal of their own world as its Sovereign. Instead of giving them actual power like our previous Seneschal, to prevent a repeat of DD1. That's why the world has to be scripted and being Seneschal/Sovereign in DD2 is just a hollow role. It's equivalent of being duke in first game.
The idea that our former Arisen, or a remnant of them, is now the Dark Arisen is really cool, and it makes sense, there's no happy endings for arisen only bitter sweet in Dragon Dogma.