I get there's a subtle difference but it's not that far off. We also say "I have 6 meters of rope". "meters" is the counting unit, which is the same concept as all the Japanese counting units.
As for the onomatopoeias, at some point you get used to them and they feel like they fit and you can start to pick them up without having them explained. Even the ones that don't seem like the make a sound, start to make a sound, at least in my mind once I've internalized it.
Not the same but in some sense similar, dogs don't say "bark" but with enough repetition many people perceive "bark" instead of the actual sound the small dog is making.