This is much more a statement about how simple the ATA port interface is than it is about Forth. Writing for hardware only <i>sounds</i> complicated to modern folks who have never tried it. Remember that these were devices built with a few thousand transistors at most. There's only so much complexity you can pack into that structure.
I would not call it "complete". Maybe "complete" in the sense that it works under perfect conditions, but not "complete" in any real sense. I don't see any error handling or power-up initialization, I don't see any DMA, I don't see any timeouts, I don't see any interrupts.<p>I could write the same code in C and it would be just about as long.