You can derive morality from observation if you aren't looking for ontological "ought statements". Hume's position assumes that the religious approach to morality is the only one possible - that morality consists of these detached and universal "ought statements" that must be observable in the Universe somehow and take on the same form as Commandments from a God.
That's not how the Objectivist ethics works, at all. There are no "ought statements" because ethics, in Objectivism, is a system of judgement and reasoning. It's applied epistemology.
So, no, you won't find a mythological ethics in reality. But you can learn how to identify the nature of things and judge how they relate, positively or negatively, to human life. And that's the essence of Objectivist morality.
But a system of morality requires the ability to make "ought" statements. Merely saying what exists is not enough information to inform correct decisions, because whether or not something exists is unrelated to whether or not it is good.
When the objectivists try to define "human life" as their yardstick for moral good, again, they smuggle in those preexisting preferences. There is no real principle that means "human life" should be condensed down to individual hedonistic comfort. It is very easy to argue that human life is better served by collective comfort, and thus the best actions are the ones that are self-sacrificing in service of the community, because these are the ones that do the most service to human life.
That's not how the Objectivist ethics works, at all. There are no "ought statements" because ethics, in Objectivism, is a system of judgement and reasoning. It's applied epistemology.
So, no, you won't find a mythological ethics in reality. But you can learn how to identify the nature of things and judge how they relate, positively or negatively, to human life. And that's the essence of Objectivist morality.