It should be noted that there are two letters in Hebrew (aleph and ayin) that represent vowels, and do not have a consonantal (is that a word?) sound. And there is a letter Y which is a sort-of vowel. Using three-letter root words, the ancient language was fairly complete. They didn’t need the complexities of modern languages; modern Hebrew, for instance, has had to add new words (“telephone”) that don’t just have three-letter roots.
My speculation, I’ve not read the Deutscher book (but it’s now on my list): the languages were initially written by being carved on tablets. It wasn’t a means of communication in and of itself, but a means of recording verbal commmunications (stories, royal edicts, etc) So if there was some small ambiguities about verb tense, say, that didn’t matter so much. Think of the writing as being like shorthand.