Hmmm I can't say I agree entirely on that characterisation of how Varis saw Zenos.
The way in which he calls him a monster when discussing him with Elidibus suggests he saw him as something worse, and not merely a royal seeking power. What I think Varis could not fathom is Zenos's mindset - his desire to seek nothing but self-satisfaction, with no further, deeper reason or agenda behind his goals, but he clearly believed there was something ghastly about him.
I kind of agree with your assessment of Zenos otherwise, but I just find him bland. He shows no reaction to the newfound powers he's exhibiting as facets of the Resonance... he's just perpetually reminding everyone of how bored he is. Fine, to a point, but he better get to one, and fast, or people are going to grow even more bored of him in turn.
I don't really care that he's got no real depth to him, but they could at least make him more entertaining. I also still believe he is going to get more than he is bargaining for out of Zodiark. His is a case of true hubris and it looks like he's simply the fulcrum to bring Zodiark into the plot without the need for all the Rejoinings to be completed.