UX is very important for backups (considering that users can be very lazy, so the least friction, the better), so a GUI is an important component; those who don't care about UX surely have infinite ways to perform their backups.

My dealbreaker with Restic was near-realtime backup - the discussion has been open for 5 years now: https://forum.restic.net/t/continuous-backup/593); this is also a UX problem. I haven't checked if Kopia supports it (or has better support, anyway), though.