For Zenos to be a successful 'pure evil' character he would need to inflict some serious lasting harm and trauma upon the protagonists. He has failed to do so and repeatedly walks away whenever granted the opportunity to do as much. So he simply falls flat as a character and seems to be have been created purely as an excuse to dismantle Garlemald without forcing the Scions or Warrior of Light to deal with the fact that an attempt to invade the place would displace and slaughter a great many innocent people.

I don't consider evil characters who only ever kill antagonists to be particularly compelling. Sephiroth was as much as a threat and thorn in the side to Shinra as he was to Cloud and his companions. Especially given what he does to a certain character...

Zenos has simply fallen flat for me. I had high hopes given the promise of an unapologetic villain but at this point I'm expecting him to do a heel face turn and side with the Warrior of Light for no other reason than 'rule of cool'. I'll be surprised if that doesn't happen - and it'll suck, given that the game has persistently refused to allow us to side with antagonists that had common ground and would realistically be open to reason and long term alliances had they not been conveniently slain/had their hands tied. Namely the likes of Regula and Varis.