Peter,
I like your rigourous approach to defining writing systems but I
wonder if it wouldn't add clarity to use morphosyllabic instead of
logosyllabary. It stresses the representation of both meaning
and sound rather than focusing on what may or may not be a
word.
Morphosyllabic as a term is also a nice parallel to
morphophonemic, the representation of meaning and sound by
analytic systems or alphabets.