I found your ideas very interesting. The comments that ensued were equally interesting. There were a couple things that I wanted to add. One of which is about Dante. When Dante fought Mundus, he was weaker than his father, Sparda. In the lore, Sparda was able to beat Mundus on his own, due to his superior strength. However, if you read Dante's bio in DMC4, it mentions that many believe him to have surpassed his father, Sparda. If Dante and Mundus fought now, at the peak of Dante's power, Dante would almost for sure, win.
Vergil, being as badass as he is, would be even stronger than Dante at this point (assuming he is still alive. He's like the Goku of the DMC universe. Always training and pushing himself) and would also be able to defeat Mundus.
On the subject of Mundus: It is implied that Mundus is still alive, and currently banished back to the demon realm (resulting effects of his battle with Dante in DMC1). Mundus COULD be re-introduced as the antagonist of a future DMC game, where (hopefully) Vergil comes back and teams up with Dante to beat Mundus in the human world, and then travel to the demon world to defeat him entirely (Can we say COOP mode?! Please?!

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On the subject of Sparda, Vergil, and Dante:
- Sparda is consistently shown to wear a purple coat.
- Vergil wears a blue coat
- Dante wears a red coat
Purple is a secondary color, made up from which two primary colors?