I feel like NPCs overshadowing the MC and not really being corruptible/ influencable outside of sub/dom dynamics is because of them being essentially commision pieces placed into the game, with their original creators having the final say in what can and cannot be done to them. And a loooooooot of them are against any kind of meddling with their concepts or corrupting them
Which is funny because fenoxo claimed, when he first ended coc, that the reason he is ending it is because he made the mistake of being to generous on the license he gave content creators. such anyone who submits an NPC is the sole owner of said NPC and they can't do anything to said NPC without permission from the owner. even though a bunch of such owners disappeared on them.
He claimed that in tits he would fix it such that he would be allowed to do whatever he wants to the characters.
To be fair though, regardless of license, the whales who are literally paying hundreds of dollars to have their precious OC DONUT STEEL fursona added to the game are not going to keep throwing money their way if they make changes without permissions.
Their fursona is a dommy 8 foot tall futa with a 2 foot long penis who ONLY puts the penis in the MC while being domme and nothing else. No you can't corrupt their fursona, no you cannot turn things around, no you cannot dedick them. That will upset the donor who paid for their fursona to be added to the game or the writer for whom it is a self insert.