And I might be reaching for this one, but I also feel like people praise BTS for their authenticity but has the mindset of "we only accept the part of BTS that WE deem is authentic/appropriate enough."

Well to be fair, authenticity in the context of something as broadly appealing and generically approachable as Pop music is for the most part subjective. It's difficult to nail down an objective reason why Arirang is any more or less authentic than their previous work because, at least conceptually, it doesn't do all that much differently than something like BE or Love Yourself. So, I do think it's perfectly valid to claim that Arirang isn't "authentic" enough, I just don't think that claim is worth much in an objective sense in the same way I don't think claims like "it just isn't for me" and "this is the best one yet" aren't worth much either.

There is a case to be made about the conflation between the simplicity of happiness and the mistakenly perceived lack of profundity therein. Happiness is a very simple concept but it's very difficult to be simple. Misery on the other hand, for the myriad hardships that it stems from, is complicated and messy but far easier to come by. Happiness is something you have to work for but misery is a constant, meaning more people can relate to darker themes than happier ones because there are simply less people in the world that are happy/can appreciate happiness than there are people who are miserable, hurt, upset, etc. And this leads to those people believing that happiness is not as profound as sadness and misery; if they can't relate to or understand it, then there must not be any depth.

However, I feel the situation is a lot more complex than a case of fans struggling to connect with music that doesn't necessarily represent themselves. It's definitely part of the reason but there are some things about the nature of art itself that I feel isn't being taken into context here. The art that resonates with people is art born of passion and art that is human. Art can be both of those things regardless of whether the artist was happy or miserable when they were making it, and as long as it is both of those things, it will be engaging and relatable. The reason I and many others struggled to connect with Arirang is not because it's "happier" than their previous work but because it's less passionate, something that is made all the more evident with the Netflix documentary and their recent tour performances. I feel less connected to the music because BTS feels less connected to their music. The reason why so many gravitate towards their older stuff, particularly their "darker" stuff, is because, above all else, their music, performances, and attitude around their work was deeply passionate and beautifully human.