I respect your opinions and thoughts on the matter of 2B/9S. With that said I'm gonna have to disagree,come on man I know you played better games where romance were carefully thought and stretched out. Nier Automata was not one of them to me,it felt so unnecessary and a plot device to try to make me care about 2B/9S. It did the opposite actually and one the reasons was their character relationship. I know 2B is suppose to be cold and calculated but playing as her she never really bantered with him and when they did it was a sentence or two with her always shutting him down or ignoring him. Also there was no noteworthy moment between them that felt special leading up to Route A's ending.
Eh, she isn't, and isn't supposed to be, cold and calculated. She is merely trying to keep distance and it is worthy of note that she fails at that too. Being E-series doesn't magically make her psychologically hardened or anything and the androids are extremely human in such aspects. The other E-type we meet in the game has gone utterly insane from the repeated acts of killing her friends all over again, enough so that she tried to rely on a mindwipe to keep the crazy at bay.
And 2B doesn't just constantly shut 9S down. When they ask Pascal for info about A2, afterwards 2B comments that it is unwise to talk with the machines without instructions from command, but also mentions that she "doesn't dislike" that inquisitive part of him, which, if you read between the lines just a bit, is her saying she likes that part of him (this might be less apparent in the English track, I haven't seen the scene with that yet) When you randomly move through the shopping mall at a later time with the two, 9S chats about shopping and the like, and 2B consents that after the war is over, they would go shopping for clothes together (well, a T-shirt to be more specific). It is kind of same with how she interacts with her operator, 6O. She tries to keep it cool and professional while 6O chatters about this and that, but still goes out of her way to send 6O pictures of pretty flowers.
The thing about their relationship is that it is already established long before we, the players, get to see any of it. 2B clearly cares deeply for 9S, but is suffering from the constant cycle of having to kill and reset him whenever he gets in too deep and we are seeing that manifesting in her attempts of keeping distance. Her is clearly pained at the bunker, post prologue, when it is revealed that 9S only managed to back up her data. It was one more valuable, shared moment that only she remembers. This repeats at endings A and B, where, realistically they'd only lose less than an hour of 9S' memories, but it still causes her anguish. 9S, on the other hand, is "doomed" to fall for 2B again and again, with him clearly retaining some vestiges of his past selves as hidden half-memories.