Originally posted by Adam Grimes
They're not really that similar tbh.
Almost a mirror image character arc in fact.
Steve starts out knowing the score. He knows the nature of the world, he knows his side is in the right, and he knows the impact he can actually have on the war is limited. His arc is leaving the tools necessary to make an impact whilst maintaining his principles and ideals.
Diana, on the other hand practically sees it as her destiny to destroy Ares. She is full of confidence that the world is black and white and that her mission is virtuous. Her arc is maintaining her mission and
Spoiler:
resisting the dark side
when she discovers the world is not as innocent as she thought.
To apply her arc to Cap, I would imagine it being the escalation of the Vietnam War. Steve is already Captain America and convinced that the United States is righteous. Only after he sees the villages being burned with napalm and women and children being shot does he actually consider his side in the war to be unjustified. Of course you have throw in some villain that will
Spoiler:
try to show him the evils of capitalism and the glory of communism while he finds some morally neutral way to resolve the conflict
.