(Pedantically) Maximum prefix length of /64 is only required if you want/need SLAAC. If you're assigning static addresses or using DHCPv6 for assignment you can go as small as you want. It's not weird to see /127 for tunnel subnets, for example.

I didn't want to encourage non-standard behavior, but you are correct. Tunnels are a common use the same way /31s can be used in IPv4.

Going smaller than /64 is against best practice and unnecessary. People coming from IPv4 need to understand that trying to be careful with subnet sizing for purposes of preserving space is not a thing in IPv6 below /64. Maybe if a residential user has a /64 from their crappy ISP settings they'd need to do it, but not in a properly configured scenario and certainly not in enterprise.