This puzzle was too easy by half. The theme, while fun to think about, wasn't much of a challenge to figure out as I went through. And the fill wasnt terribly challenging either. I once had a theory that the Sunday puzzles went through a rotation of difficulty over the course of a month. I didn't have the wherewithal to follow that theory through, but if I was right, this puzzle was on a Monday level for me.
In terms of the theme, I liked REALNUMBER the best. This seems the most correct of all of the answers. My daughter is learning about imaginary numbers right now, and it's a fascinating topic. I also liked SNAILMAIL and SILENTFILM. PAPERCOPY was my least favorite. Perhaps it's the clue. It's not exactly correct that electronic documents made the use of "paper" before the word "copy" necessary. I'm not sure what would be better, though.
1A: "The cauldron of Democracy" (AMERICA) gets a D for all the ways in which that cauldron is currently failing. Boy, I wanted something to do with classical Greece for this answer.
Overall, I felt the fill was smoothly done. I liked the four long down answers that anchored each corner, with COWTIPPING being the best by far. I'm also a fan of UNHANDS and THATHURTS. Best clue goes to 51A: Cackle from a greedy person (ALLMINE).
I don't entirely believe in TOPRANK as a thing people say. Other unhappy fill includes ETDS (plural? really?) and CTS, which is an abbreviation that no one has ever used.
I continue to be amused by ISIT? ITIS.