Okay so... I don't totally belong here because although I know bts' names, basic facts about them, and like a few songs, I know very very little about their ships. So this might be my only comment, because I don't want to derail this thread, but I do want to talk about the kpop ship I always thought was "real".
I've been a kpop fan since 2012 and my favorite group is shinee. My biases are jonghyun and kibum. And the ship I always thought--and still do believe that "something happened between them" is jongkey.
Most people believe that their relationship fits the first option you talked about, they believe that from 2008-2012 they were more real. I shipped them from 2012-2017 so obviously I don't believe that, but I do believe that back then their moments were more childlike, and instinctual.
During their predebut days, jonghyun and kibum were friends even when they didn't know they were going to debut together. Fans of smtown trainees said they were always together, and that jonghyun was basically kibum's shadow.
So regarding bts pairings, I think it's definitely smart to ship the ones who hung out a lot together during predebut. Because as cutthroat as the industry is, we all need someone to lean on.
In 2013/2014/2015 there were less obvious jongkey moments, but there were way more hidden moments, which is why I continued to ship them, because they kind of shifted into the second option you talked about, they are older, and they seemed to have more of a choice.
The last really... powerful jongkey moment, was when jonghyun had given kibum a ring for his birthday in 2017. Of course they weren't married and of course they couldn't get married, not in korea at least, but... I still feel so bittersweet about it. It felt almost like a promise of something more, something /real/ and it really made me think "wow this five years of shipping was finally worth it". The end of 2017 was a tragedy, and I dont want to make my comment too sad, but I felt so bad for kibum. And I felt just as bad for jinki, minho, taemin, his family, and his friends but... the way i felt for kibum just felt... different. I dont know how to explain it. And he had to mourn in front of everyone and fans were making it worse by writing "jongkey" on every single post he made.
Later in 2018, kibum made a solo album/debut that, in some ways, reminds me a lot of jonghyun's music. He has a few songs that I would call "couple songs", where it seems like he thought about jonghyun's songs and "answered" them in his own songs. In 2019, his repackage for his album has some aesthetics in it that look like old pictures jonghyun took over the years.
So, yeah. When it comes to real person shipping, I never want to annoy the people I'm shipping so I am very selective about this stuff. Jongkey is the only relationship I have shipped, without them actually saying "we're dating". And for a lot of these ships we may never get that, but I think sometimes you just *know*.
Also! To be completely honest I think their relationship was like an "open secret" amongst other idols, because when an idol would mention kibum, they'd talk about jonghyun too and vice versa.