It is normal that devices will use the link-local address as the gateway. In general, when devices talk to other devices on the same LAN segment, they're going to use the link-local addresses and not the globally-unique routable addresses (public addresses). It takes a little getting used to, but it makes sense when you start to get the hang of it.
Also - the router isn't providing the address, it's advertising the local prefix. It's the client device which chooses an address for itself from within the prefix of the advertisement. Routers send the RA messages using their link-local addresses, and the client device will simply set its default gateway to be the link-local address of the router whose advertisement it heard.
When given a spoon,
you should not cling to your fork.
The soup will get cold.