Earlier quoted context omitted.
At least for me, the mechanical skill with the pencil does hold me back for non-organic shapes. I have trouble sketching things I can see clearly, but its not significantly harder for things I am only familiar with. For example, if I tried to sketch my bike, I would have no trouble getting the structure correct, but I would have trouble getting smooth wheels.
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.