Back in the day demos were more impressive imo. A lot of them now use direct x or opengl. For the most part the stuff you see isn't written by hand anymore AFAIK, they just have programs to generate the actual demo. Basically they use modeling programs.
While true for large demos, the 4kb — perhaps even 64kb? — are still written very much by hand.
I hope so. I'm not involved with the scene at all, but I did read a bunch of history about the scene and watched tons of demos.
I think farbrausch was one of the major groups who did this sort of thing https://github.com/farbrausch/fr_public