To be honest, I do agree too with all of the reasons above and while I do see the pairing as Yuri and all of that, I think that most people who'd want to deny any romantic relationship between these two have the valid argument of saying that Nadie looks a bit more like a "guardian" figure or even a parent for due to Ellis childlike personality. But yeah while I do agree that the authors aimed for a more romantic relationship, be it canon or not the show is one hell of an enjoyable ride.