Varis' unwillingness to work with others is a product of his
immense arrogance. Like I said earlier, that
one line from him in the Sea of Clouds...
"'tis my solemn charge as Emperor to bring the eikons to heel."
... tells you everything you need to know about his character.
To put it in a more vernacular way:
"I'm the Emperor now, so it's my duty to protect the world from eikons."
He doesn't trust anyone else to accomplish this task and has no interest in cooperating with others to do so - why would he? He's Emperor, he knows best, and what's best is for everyone to listen to him and do what he says. To use another piece of media for reference, this makes Varis rather like Zamasu from
Dragon Ball Super - he doesn't believe in anybody but himself.
That's how overwhelmingly massive his ego is. And, much like Zamasu, I don't think he'll have a change of heart either... unless his collaboration with [probably] Elidibus ends with him getting fed a whole humble pie.
Now, we can recount all the terrible things Varis and his country have ordered and/or actually done, but they still have that thin veneer of "for the planet's survival" to fall back on... making them not objectively evil. However, that's all it really is - a thin veneer, or to put it in a more vernacular way, a pathetically obvious excuse. We know,
for a fact, Garlemald would still be grinding its war machine against the rest of the world without that excuse. A lot of its cruel ethos has nothing to do with eikons. ("They're cruel to others because they were
naturally disadvantaged horrifically persecuted before they developed magitek!" - That's irrelevant.) It
tried to commit genocide on the entire subcontinent of Eorzea with Meteor, which would have been
orders of magnitudes worse than what Sylvanas did to Teldrassil. (I'm still curious as to why everybody puts the onus for that debacle solely on van Darnus when Solus had the final say. "Not all Garleans agreed with the Meteor Project!" - That's irrelevant.)
... nonetheless, however much I may disagree with its ethos and goals, Garlemald and its Emperor cannot be condemned as pure, straight evil because of that thin veneer - that ostensible proclamation that what it does is for the survival of the planet. I oppose it on an ideological level and condemn damn near everything it does, but that doesn't make it Grade-A "Evil."