An "honest" human aligned AI would probably pick out at least a few bronze age morals that a large amount of living humans still abide by today.
Absolutely nobody, because no such concept coherently exists. You cannot even define "better", let alone "best", in any universal or objective fashion. Reasoning frameworks can attempt to determine things like "what outcome best satisfies a set of values"; they cannot tell you what those values should be, or whether those values should include the values of other people by proxy.
Some people's values (mine included) would be for everyone's values to be satisfied to the extent they affect no other person against their will. Some people think their own values should be applied to other people against their will. Most people find one or the other of those two value systems to be abhorrent. And those concepts alone are a vast oversimplification of one of the standard philosophical debates and divisions between people.
> Did not a transcendent universal moral ethic exists outside of their culture that directly refuted their beliefs?
Even granting this existence, does not mean man can discover it.
You belief your faith has the answers, but so too do people of other faiths.