The visual density of Japanese characters has more to do with the fact that it's not a requirement to have white space between words so you can line break mid word. The characters also don't change in size (no real upper or lower case) so everything is pretty mono spaced.

For example look at the wikipedia article for mother in english vs Japanese

https://ja.wikipedia.org/wiki/%E6%AF%8D%E8%A6%AA

https://en.wikipedia.org/wiki/Mother

In the English sections with pictures there's significantly more white space between the text and pictures than in the Japanese version.