I mean, the point was definitely stated as protecting creators. We’ve seen some solid David Vs Goliath stories of artists taking people who steal their work down.
However, this isn’t the reality for the majority of copyright. A lot of it just ties up works to companies owned by speculative shareholders (think of the lord of the rings).
Limits to duration would definitely help this, and we’d be on the same page there. However, I do still wonder if it shouldn’t be shorter for certain things (e.g. medical treatments or manufacturing), with the option of a public domain buyout to cover (reasonable, non-inflated) research costs.
Ehh no, you genuinely can’t patent any form of mathematics.
Mathematics falls under “exists in nature” (if you are a Platonist) or “abstract ideas” (gets even clear thinking Constructivists). So they’re excluded from parents and copyrights no matter how complex the system
Textbooks usually belong to the publisher (academics commonly have to pirate their own papers), so that’s usually a bust.
You might be able to patent an algorithm associated with a branch of mathematics, but that’s trickier than you think. Blank slate development can, and does, happen (see Compaq’s reimplementation of IBM’s bios). You’re banking on it not being reversed engineer able (spoiler, don’t take that bet if you’ve published your proofs!).