Belief in an all powerful external being such as an Axial Age God or the modern incarnations such as neoliberalism might not have brought a lot of happiness to the world...so what is the best way of not believing?
The best way would require the least amount of effort. Which is why proving that you must be an atheist isn't as good as showing that even if one does exist, it's irrelevant that a very powerful external being exists.
An external monotheistic deity couldn't be omniscient, omnipresent or omnipotent according to OOO.
It's better to think this as a non-theism rather than atheism. Many atheisms are still shadow monotheisms.