Hello Daniel
Yes, you are correct about the prefixes, they should be higher as you say. I have since corrected my previous post.
Now concerning the prefixes delivered by ISPs, there is no hard and fast rule that says that ISPs must deliver /64 prefixes or /48 prefixes. These are general guidelines that many organizations do follow but not all. Also remember that the ISP that delivers the prefix to the end customer may also be a customer themselves, of another ISP, from whom they purchased the IPv6 address space. So they may have been provided the /48 which they break down further into /64 for their customers.
So it really depends on the policies provided by your ISP. Keep in mind that the various sections of an IPv6 address, that is the global routing prefix, the subnet ID and the interface ID are actually of variable sizes. You can see more detail in the following post as well.
Finally, about the use of link-local addresses for routing protocols, routing protocols can actually use global unicast addresses as next-hop addresses, but that’s not the default behavior of protocols such as OSPFv3. You can for example create a static route to a global unicast address and it will work just fine.
I hope this has been helpful!
Laz