Springboard and Control Center customization alone are worth the upgrade, but also:
- loads of small Safari improvements (reader mode, the way extensions are handled, "removed distractions") add up to a really huge upgrade that I'd never go back on
- remote-screen for iPhone on Mac
- RCS support in Messages
- emoji tapbacks on Messages (it's silly but I like it and long overdue)
- Passwords app
It adds up. iOS 17 would feel very backward to me now.
He's specifically asking about 18.1. All the things you listed are in 18.0.