Microcontrollers and software for consumer PCs and the like could have been produced, probably, but there are a lot of areas of deep specialization. You'd have had to bring together all sorts of different disciplines and technologies the old, hard way - universities and libraries and researching manually. The internet allowed all of those things to coalesce easily, and novice level people gained access to high quality information and research at the click of a mouse.

The patents, compute, research access, and dozens of other relatively small barriers created a thicket of challenges and no obvious way to reconcile them, even if you had all the right ideas and inspiration. I think the internet would have been needed in order for all those ideas to come together in the right way.

paper printers only needed such accuracy in one axis of motion, and had gearing to provide it.

hard drives use voice coils, a completely different technology. The circuitry that does that evolved and certainly influenced the creation of microstepper controllers: the neat trick they do is treat the stepper motor as a voice coil in between full steps.

"cheap consumer paper printers and hard drives" was not a 1970s thing.

I mean, towards the end of the decade was something like the ImageWriter, which let you do bitmapped graphics, as a row of 9 dots at a time. At https://www.folklore.org/Thunderscan.html?sort=date you can read about the difficulties of turning it into a scanner. (Like, 'We could almost double the speed if we scanned in both directions, but it was hard to get the adjacent scan lines that were scanned in opposite directions to line up properly.')

The LaserWriter wasn't until 1985 or so. My first hard drive, 30 MB, was a present from my parents around 1987.

By the 1996, laser-based 3D printing based on cutting out layers of paper was a thing, available for general use in one of the computing labs in the university building where I worked.

The result smelled like burnt wood.

When I visited a few years later they had switched to some other technology, and one which could be colored, but I forgot what.