First thing I want to point out is by making an ethical judgment on the God of the Old Testament, it does not demonstrate whether he exists or not. It’s not logical to complain about the moral attributes of an entity if that entity does not exist. I’m not going to go around complaining that the flying spaghetti monster is an evil monster and violates basic human ethics. I don’t even believe the FSM exists so why should I care what attributes it has? This pretty much goes for any claimed deity. I don’t care about the lustful habits of Zeus or the cannibalistic tendencies of Cronus or the self-mutilating character of Chhinnamasta.
However, the attributes of a god would matter if it leads its followers to act unethically. One can rightly complain about such a belief of that religion. But, it is still possible that deity exists, even if one doesn’t like its ethical attributes or what it teaches. For example, Christians believe the devil exists, but they do not like his attributes.
Bottom line, the moral characteristics of God cannot demonstrate He does not exist. But moral characteristics is relevant if it leads to unethical behavior of its followers.