This writing is sort of a strange metaphor, but I guess the point the author makes is that kanji can be transliterated as hiragana but not katakana. The writer goes on to talk about traumatic brain injuries so I guess he's aiming at the cultural value of each syllabary.
I'm not a native speaker, but if I were to make an equally strange metaphor as the author, katakana feels like writing in all capital letters.
Kanji can be transliterated either way, and both forms are lossy since there are so many homonyms and kana only encodes sounds. It's traditional to annotate difficult Kanji pronunciation with small Hiragana called Furigana, for example in children's books. But it could be done all the same in Katakana. Modern Chinese words that Japanese borrows are usually translated in Katakana for example.
Kana mostly contain just sounds, but do contain some morphological information—there are homonyms in kana as well, after all. This is a bit rare, however.
I'm not a native speaker, but if I were to make an equally strange metaphor as the author, katakana feels like writing in all capital letters.