Given the resources you have already listed, I’m not sure there’s much to add.
For your first bullet, the article, “Essence of Scala”, starts with the “DOT Calculus”. I don’t know where you could find a discussion about how that’s related to the more Math’s general notion of “calculus”. Perhaps someone who was involved in the DOT proofs could show an explicit connection.
For your second bullet, it appears all three articles you cited provide first approximation answers to your questions.
For example, Odersky outlines the elevated expectations of performance improvements because of the resulting simplification of internals. Whether that is from improved type soundness, or the many other Scala 3 adaptations and improvements over Scala 2, or both, it’s not clear. And what benefit would there be from seeking clarification?
Were you intending to use Scala 3? Or are you researching it to consider as an option against other alternatives like TypeScript, Haskell, etc.? Or are you just a compiler theory enthusiast just kicking the Scala compiler tires as opposed to seeking to actually utilize it? Just trying to continue to narrow down what you’re actually seeking as your questions still left a very large abstract surface area.