For an antagonist to be bereft of redeeming qualities I think they need to be a credible threat to be interesting. I'd get bored rather quickly if we're due yet more expansions where we're stuck with an immortal main cast and the only causalities are the occasional throwaway character or other antagonists.

Zenos was - by Yoshi-P's own words - intended to be utterly lacking in redeeming qualities and yet in the end he never once actually killed anyone of note. He was just exploited as a convenient plot device to help deal with Garlemald off-screen and devolved into fawning over the player character like so many other characters already do already.

Personally I quite like shades of grey and nuance - I just prefer it when a setting can commit to it with consistency. A good game also arguably pleases fans of both the protagonists and antagonists alike - since personal tastes differ significantly and it's often quite subjective as to who is a 'hero' and a 'villain' when a story is complex enough.