Hmm I'm not sure you're completely clear on how syllabaries (including katakana, hiragana, kanji, etc) work. You can use them to encode anything as well
Orthographic English is probably the best example to show the inefficiencies alphabets sometimes bring. The English language has ~24 constants which are often well-represented, but then you have things like "ng" or "sh" which is actually a single phoneme that we lack a symbol for. On the flip side, English has an unusually large number of vowel phonemes, around 13 monophthongs and 7 dipthongs. Yet we have only 5 symbols for vowels and often use them in very ambiguous and end up having strange combinations of them leading to ghoti:
The point is you only have 26 letters, but now you end up having to memorize a vast array of combinations and how they work in different contexts. You're really not saving yourself any more memory space than if you'd learned a syllabary
Orthographic English is probably the best example to show the inefficiencies alphabets sometimes bring. The English language has ~24 constants which are often well-represented, but then you have things like "ng" or "sh" which is actually a single phoneme that we lack a symbol for. On the flip side, English has an unusually large number of vowel phonemes, around 13 monophthongs and 7 dipthongs. Yet we have only 5 symbols for vowels and often use them in very ambiguous and end up having strange combinations of them leading to ghoti:
https://en.wikipedia.org/wiki/Ghoti
The point is you only have 26 letters, but now you end up having to memorize a vast array of combinations and how they work in different contexts. You're really not saving yourself any more memory space than if you'd learned a syllabary