It isn't really true that DHCP and DNS are coupled, it's just a common feature for power user routers as it's convient.
There are options for IPv6: PFSense, as an example, has "Assisted" RA mode where devices can use SLAAC or DHCPv6, so you have SLAAC for general clients that don't need more (e.g: phones that don't support DHCPv6), but clients that want more can use DHCP to provide specific reserved addresses and DNS names, etc...
There are options for IPv6: PFSense, as an example, has "Assisted" RA mode where devices can use SLAAC or DHCPv6, so you have SLAAC for general clients that don't need more (e.g: phones that don't support DHCPv6), but clients that want more can use DHCP to provide specific reserved addresses and DNS names, etc...