Instead of axis which treats law and chaos as fundamental principles, the outer planes are divided along the lines of social order vs personal freedom. And instead of good heavens and evil hells, the division between the upper planes and lower planes is one of peace vs violence.
Good and evil, then, become positional. Baator is the plane of social order enforced by violence, and they think they are the ultimate good, because they have strong values, and the courage to defend them. They like Mount Celestia, because it is a place where filth and corruption are expunged from the souls of petitioners, but they don't respect it, because Celestia doesn't force anyone to climb its slopes, and it offers its benefits to enemies and allies alike. They view Arborea as the ultimate evil, because it represents decadence, where any perversion is indulged, and the utter lack of discipline has made its residents weak and puerile. The Abyss is hated, because they too represent the destruction of civilization and order, but they are marginally respected, because they at least have the backbone to fight back.
In this imagining, the lower planes view themselves as the armies of the upper planes, holding back the tide of fascism/anarchy that would swallow those peaceful places whole. They view the upper planes as their natural jurisdiction and territory (although in different ways - Baator would unite the "lawful" planes into an Eternal Order ruled from the heart of Malsheem, whereas the Abyss would have the "chaotic" planes as their own borderless playground), and will get around to subjugating them once the threat has passed.
The upper planes view the lower planes as a regrettable necessity, and terrible tragedy. They could all be saved, reformed, and enlightened, if they would just put aside their hatred and fear, but because they can't, it's inevitable that they would find each other to fight. Because they're defined by peace, they don't necessarily wish to exclude the "other side," but they certainly believe that their partisans are closer to salvation (for example, Arborea thinks that the Abyss would be fine if the Tanar'ri could learn to do their own thing without hurting others, whereas Baator is practically built out of the sort of coercion that is anathema to them).