"Half the drive's recording heads will operate together as a unit, while the other half will operate independently as a separate unit,",
"The host computer can treat a single Dual Actuator drive as if it were two separate drives,"
And so what you've got is one disk enclosure, and one interface, but effectively two independently operated drives. Not two independent read/write arms accessing the same entire disk. To access a particular set of data, you are still waiting on the queue of commands for a single arm. Ho hum.
We've got to look for something like the additional word 'parallel' to get the nirvana of "times N" access to one set of data. Though duplication of data using RAID may help? Oh, that's reads only.