You don't have to draw freehand. A t-square, a pair of compasses and a set of French curves are pretty much essential if you want to accurately draw precise geometric forms.
You also don’t have to draw “free eye”. There are plenty of tools you can use like tracing paper, photographic references, coloring books with the lines already drawn, ...
None of my illustrator friends use french curves or compasses to do their sketching, and usually even skip using a straightedge, but through practice can make very nice straight lines, right angles, circles, other curved lines, etc.
Hand-eye coordination at the level that professionals have takes an incredible amount of training/practice. It’s hard to imagine how you would even disentangle their practice at mental visualization vs. practice at proprioception, etc.
Most people can accurately trace a line drawing, but can't accurately copy it by eye. Try it for yourself and you should see that your manual dexterity isn't a meaningful bottleneck in your ability to draw.
Drafting tools might well be a crutch, but they were considered essential in the days when engineering drawings and technical illustrations were routinely done by hand. If you need to use a spline to draw smooth curves or construction lines to draw perspective, so what?
By the same token, if you need a computer to draw [this or that] so what? Or for that matter, if you need to hire a trained draftsperson to do it, so what?
> Most people can accurately trace a line drawing, but can't accurately copy it by eye.
Yes, tracing a line drawing has much more direct feedback. The correct line is right there, and there is no need to synchronize imagination with hand movements. (Untrained people are still very slow and error-prone at tracing though, compared to professionals.)
In a similar way, people have an easier time playing a piano tune if you directly show them which notes to play on a physical piano a few at a time right before they press the keys themselves vs. if you let them hear a whole tune and then try to play it from memory a few minutes afterward.
That doesn’t make piano playing an “almost entirely audial skill, with almost trivial mechanical skills” involved.
> That doesn’t make piano playing an “almost entirely audial skill, with almost trivial mechanical skills” involved.
I'd say it does. I have terrible hand-eye coordination but can play piano at a decent level (whereas I'm distinctly bad at e.g. tennis). Playing a piece I already know on the violin on the piano (or vice versa) is a much simpler exercise than learning a new piece from scratch.
