Is running it with an admin interface an option? I'm looking for a good CMS I can deploy for others (less tech-inclined) where they could still make their own small changes.
Yes both have admins and as i wrote in coments around i think admin is what makes kirby highly superior.
We always have problems with clients not being able to edit things in wordpress.
In kirby its possible to do in much simpler way. Basicaly you create admin that has only the content. No settings and user managment and all kind of useless functionality..
Grav is fine too but users will have to learn a bit more. Its more clunky and not so dumbproof.
In all of the filebased cmses the admin and the core are separate. Core renders stuff from files. Admin is just for creating/editing filest. They dont know about each other.
It's insanely awesome and open source. No database needed either. Can also run more like a static site generator, without admin interface.