Well, over the XS you get lots of little incremental improvements that will add up:
- bigger screen in a thinner, lighter package
- Slightly refined design, if not earth shattering.
- Brighter XDR screen
- Longer battery life
- 5G
- better water resistance
- A14 chip
- Better protection from drops
- New MagSafe accessories
If you're coming up on a standard 2 year replacement cycle, you get a fresh battery with the new phone as well, and at a £200 discount over what you paid for the XS.
I think I get what you mean in the OP though, you think Apple puts too much effort into the camera to the neglect of other improvements? It does sometimes feel like that, but I think it's more that the camera is one thing they can improve year over year that a lot of people actually do care about, while phones in general have reached a bit of a plateau in other features.