Problem with syllabaries is that you end up with excessive symbols (Japanese phonetic “kana” have over 50 symbols, and you don’t get away with not having digraphs); you have the problem of terminal consonants, especially when your syllabograms always end with a vowel sound.
Nope, the Gojūon (kana table) translates literally as "fifty sounds" because there's the ten consonants times the five vowels.
Five of those combinations don't exist, there's the stand-alone 'n' and two voicing markers for a total of:
50 - 5 + 1 + 2 = 45 + 3 = 48.
So, less than fifty. (There's two forms: hiragana and katakana, but that's kind of like upper and lower case, so I'm not counting that.)
you have the problem of terminal consonants,
Granted; though the Japanese pronunciation is a very soft/nonexistant vowel-sound on -u ends. So "desu" would be pronounced 'des'.
you don’t get away with not having digraphs
True, but there aren't any surprises in the digraphs. (ex: no p + h —> f or t + h —> th [rather than t'hu].)
Well, kana spellings are always obvious; if you can pronounce it you can spell it without fail. Trying to transliterate from languages that feature terminal consonants causes a problem, but then the alphabet wasn’t originally designed to allow for that.