If we can't have one, we will have two, or three, that's what the context is for. Also, we have our own dictionary, we don't need to consult chinese to know the meaning of vietnamese words.
In the end, it's still way easier to write and learn Latin alphabet than studying chinese characters, that's an advantage in itself. In the future, if we find something better, we will switch to that too as long as our distinct sounds are kept.
As I said, Vietnamese love sound, we love talking, we don't love the writing character for the sake of it.
EDIT: Chinese are also contextual, just dropping random word doesn't mean anything, if I write just 漢, you don't know if I mean the race or the dynasty.