To me corruption is about being selfish; which is or par with dominants, and/or being depraved; which is on par with both submissives and dominants. And like you stated, high corruption pcs being able to drink cum out of Elthara's ass, that's depraved, and we see a few other options like that. What we don't see is the selfish side, like in CoC1 where we could feed Amily transformatives mixed with cum to essential turn her into a sex slave.
Just to clarify a bit of the idea of domination
I personally find the idea that domination is corruptive and a characteristic of a corrupt MC/NPC to be totally bonkers, I'm a dom in a bdsm society and I can tell you that domination can be more about caring than most people would think, not only do a dom need to understand its sub whishes he also needs to care for his/her well-being, the power a dom has over a sub is not taken by force, its earned through love and trust
Of course there's always people that go overboard and end up doing shit like unnecessary violence, but those people are seen as selfish assholes, as stated earlier, and even criminals sometimes when things go really bad
I seriously think of coc2 as a game to play when it's late at night and I have nothing better to do, the way almost everything is implemented in the game sucks so hard that I'm actually losing interest in the game, if it wasn't for Kas and a few npcs here and there that I still have hope for I would have dropped coc2 years ago