Many dictionaries have the definition of atheism as being the belief that gods don't exist. Additionally, I have never encountered anyone, outside of here or a philosophy class, who thought that the word "atheist" primarily referred to anyone who wasn't a theist. It is always, in my experience, been a word associated with the belief that gods don't exist.
So when you say "it's what the word is", that is not quite correct. Right now, the "lack of" definition appears to be a newcomer, that has gained popularity primarily within the atheist ranks.
It's not good enough to say that the word "isn't really going to reveal much by its nature." We are discussing the nature of the word. Your argument is circular.
Why do you think that the word shouldn't reveal much? What benefit is there to such a position? Why do you think that everyone who isn't a theist should be called an atheist; why do they all need to have a label (and especially one that essentially states nothing)?