Unlike many other characters in FE history, Zephiel had Guinevere and presumably other people outside his horrible parents. His dad was awful, but he could've just...left. That was an option. Hell, Lewyn did it and there's plenty of other FE characters who just went "Fuck this shit, I'm out." He could've gotten himself a dragon waifu and settled down somewhere. Desmond wanted him gone anyways. The more I look at his character the less sense his actions make.

He just doesn't work as an enemy for me. Maybe if some remake made him fallen or corrupted by Jahn or something.