Even on Solaris the ARC existed. ZFS replaces a lot of systems traditionally not directly related to a Filesystem implementation.

For instance using the `zfs` tool one wouldn't only configure file system properties, but also control NFS exports, which traditionally was done using /etc/exports.

This was done as part of major UI/UX reshaping in Solaris 10 to make sysadmin lives easier, what it ultimately does is... Edits exports file..

ZFS and ZPOOL tools provide accesses to multiple different subsystems in ways that make more sense to end user, a lot like LVM and LUKS do on top of device mapper these days