If a god exists, its mere existence can't logically define morality. Might doesn't make right. No one being defines the morality of every single living thing because rules and laws aren't morals. Morality doesn't have an "opt-out" option either. So either the god that supposedly exists is subject to the same moral principles, or it is doesn't behave morally considering the stories attributed to it.
What then is more likely? 1) humans assigned the morals/rules/laws that they wanted to govern their society to a god so as to try and assign their morals/rules/laws to some sort of unquestionable authority? or 2) a god exists but created a set of objective moral standards that aren't actually able to be objective in practice and that change through time in such a way so as to conform to the evolution of moral values through time?
What then is more likely? 1) humans assigned the morals/rules/laws that they wanted to govern their society to a god so as to try and assign their morals/rules/laws to some sort of unquestionable authority? or 2) a god exists but created a set of objective moral standards that aren't actually able to be objective in practice and that change through time in such a way so as to conform to the evolution of moral values through time?