For me, I think of spells and the magic slots as being an in-game thing. The magic stuff comes up as interactions in a lot of games (wizard spell trading, PCs planning based on their resources, etc.) I have played in and it would be a lot of work to narratively obscure the mechanics out to an abstract level that is not physically present. If someone asks the mage why they didn't cast another web out of spell slots is one easy answer, obscuring answers are other possible ones with some issues.
Superiority dice I don't think of as a discrete narrative element of the world but as more of just a mechanic. If someone asks a fighter why he did not hit the monster harder the response will be either 1) I am trying to, or 2) shut up. I can't imagine someone saying in-character why didn't you use a superiority die there. There is nothing physical in character there that is really identifiable as the bonus die the way a web spell is there.