Oh my gods, I pinpointed exactly what it is that makes Aeon a non-ship for me. Rewatching their speedboat ride in RE4R, and he says "I've changed." And Ada says, "You haven't changed. You just think you have."
It's not Doctor and River Song energy, I was wrong.
It's Eris and Sinbad energy.
A heartless, efficient woman who is intrigued by this man against her better judgment, so she can't help getting involved in his life and luring him into her business. And if she allows him to say he's changed, that simply highlights that she hasn't. /Is unwilling to. So she rejects it, saying he hasn't changed even if he wants to have.
But Sinbad did do the right thing, regardless of Eris' desires.
And Leon did change and grow, and also hasn't lost that sterling silver moral code. So there it is, the contrast that confronts Ada with how dark she is compared. At least Ada reroutes the chopper at the end. I give her full credit for that. She can't help but let him change her in little chipping efforts.