I love this! It was super fun reading your thoughts on this and a lot of points I agree/thought myself. I definitely suffer this dissatisfiaction with my lineart/sketches. But I always find to be less an issue when my lineart is "doodle" quality/quick when Im not trying to do pristine lineart. I think half the problem is during linart people tend to get more stiff and less fluid in pursuit of perfection. Def happens to me a lot!

Love this, you definitely put it into words better than I could. Our brains like to fill in the dots by themselves and definitely do see what they want to when given more ambiguity. Wildly different topic but it’s SORT OF the same reason why you don’t explain a horror monster 100% of the way to your audience because if our brains fully understand something it becomes a lot less scary (read: less interesting, usually). It can be really tough for me to keep that lively-looking illusion of motion while using super clean lines. I find using all super different line weights for different parts on the character helps a LOT with keeping my line art as visually engaging as the sketch was, personally