diskutil is for disks (e.g., volumes) while hdiutil is for disk images ("file system as a file"). They're not two versions of the same thing, so it doesn't make sense to dub deprecating hdiutil as "progress."
Nobody really cares that they were originally for separate things.
A disk image is not just a fancy disk. Disks and disk images operate on different planes, which is why the distinction between diskutil and hdiutil exists.