Comment by T-R

A lot of material for younger readers uses similar spacing to Korean, like the Pokemon games. It works well enough when you know the vocabulary being used is limited, but even there it gets frustrating.

When you're reading, you're trying to identify a substring and map it back to the unit of meaning, which is effectively the kanji. That works seamlessly with Hangul, because it mostly blocks (as syllables) the same way as kanji, and, as you mentioned, the extra vowels and silent consonants provide more disambiguation. With kana, the length you have to scan to read, and then guess at (using only context to disambiguate), a root word, is a lot more arbitrary.

Mechanically kana is just less compressed, less aligned, and makes it harder to visually identify/scan for units of meaning. Obviously Korean shows that you can make different tradeoffs, but for Japanese losing the kanji would probably necessitate reworking Kana as well - and unless the pronunciation changed, it would probably need to be in a way that represents the pitch accent, which is a modifier on the whole syllable, rather than just a few extra consonants or vowels.