My children are Japanese-English bilingual and can read far more advanced books in English. Initially I took this as an imbalance and suggested they read the same books (or something very close) in Japanese. But their native Japanese language teachers said, no, because of the different learning curves you can't expect them to read the same level of Japanese texts; the equivalently educated/advanced Japanese reader will be behind, at least in the elementary school years.

Japanese as a whole are extremely avid readers, so I don't think there's a gap at the top, only the shape of the learning curve.