Syllabic versus Alphabetic Scripts

[Narayan R.Joshi]

To the best of my knowledge, Devanagari is syllabic script while Roman is
alphabetic script. I do not know the category of the ancient Indian Brahmi
script. Is their any reason for the ancient Indians going in the direction
of syllabic Devanagari instead of alphabetic script? Devanagari produces
almost all sounds of Sanskrit faithfully. Was this true of Brahmi? Was
Brahmi ever used to write Sanskrit? When did the Granth script of South
India come into existence? What is the earliest inscrition(or writing) in
Devanagari found in India? I read that Vietnam has Devanagari inscription
from 8th century AD. Thanks. N.R.JOshi.