The problem is, who defines what "moral best" is? WW2 German culture certainly held their own idea of moral best. Did not a transcendent universal moral ethic exists outside of their culture that directly refuted their beliefs?

> The problem is, who defines what "moral best" is?

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.

No need to drag Hitler into it, modern religion still holds killing gays, women as property, and abortion is murder as being fundemental moral truths.

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.

AI race winners obviusly.