So am I, as a terminal user, supposed to track file handles now?

CLI programs might be used by an actual human, not necessarily called by a script.

UNIX/Linux already has a compromise here with stdin/stdout/stderr, the convention that those are fds 0, 1, and 2, and stream redirection in shells. You can already redirect raw fds in bash on linux, that's exactly what "something > something.stdout.txt 2> something.stderr.txt" does.