No, not about the system of power, though that's necessarily related. More like: If the Leviathans are going to create a thoroughly nasty universe, then why do they want it? What's the point?
I'm sure that's a good question, but I'm still not sure what you mean. If it's that they're creating an unpleasant world for themselves, it would physically be a better environment... Mean people manage to have a lot of fun being mean, or at least a lot of satisfaction. It's temporary though and they keep having to find people to be mean to, even after they've killed all their enemies (and I do think humans are important enough to them to enjoy slaughtering them), so I think in an all-Leviathan world, they'd end up turning on each other, which might be how they left this world in the first place.
Being
that mean isn't really a choice. If you're twisted enough, you're too far gone to find your way back out. You're just sort of stuck with it, and you have to look for outlets. A world of vicious snakish creatures isn't ideal, but if you're one of those creatures, that's as good as it gets.