While I do agree with you on the spoken side, there was a comparative study of spoken syllables per language floating around at some point [0], is this really true for written Japanese ? As each kanji is potentially multiple syllables long when spoken but still one character when written, conveying a meaning of itself. (I'm simplifying here obviously, as there are kanji combinations to give a specific meaning, eventually modifying the number of syllables when spoken and others)

[0] : https://advances.sciencemag.org/content/5/9/eaaw2594