I do believe perceptual bias is relevant, even though it is indeed partly* a side-effect of the physicality I mention. And it's not harmful, in fact it's crucial to good design. My objection here is to the way some people give primacy to the origin tool. This is a romantic historicism that misdirects and/or stunts progress because a tool –especially when it has stopped evolving– is much more of a ball & chain. So freely conclude for example that Arabic should have horizontals thicker than verticals even in a "monoline", but don't keep using the now-circumstantial origin to justify it.