Anyways since I've grilled you on your interpretation all day, I think it's only fair I offer mine. I think this line right here is one of the more important ones. Since it came directly from ZUN himself and not other characters in game.
"One of the strongest youkai living around the Hakurei Shrine. Her personality is such that one can never tell what she's thinking, so she's a very uncharismatic youkai. However, she actually seems to be quite sharp-witted..."
I think she's just really misunderstood. She's misunderstood time and time again. In LLS, she IS actually wrongly accused of being the destroyer of Reimu's shrine. As for MS, the demons were genuinely an issue that everyone agreed needed to be dealt with. I think calling what Yuuka did in makai a "genocide" is completely unreasonable considering Marisa (a character never even close to being memed as a sadist) did the exact same things as well. She genuinely wanted to go over there and test out her powers against some of the strongest, and it was just a convenient excuse since nobody liked the makai demons anyways.
Come PoFV, she's mostly the same, but perhaps a bit more self aware even. Everyone thinks she's a monster once again, and she just rolls with it instead of trying to correct literally everyone's preconception of her. Even if she had stayed in the garden of the sun, people would've come after anyways, which is exactly what happens when you don't play as Yuuka. So why not have a little fun? Akyuu's profile is her is really awful as well, which has been said countless times and isn't even worth repeating.
She is polite to others, but only when they don't know who she is. Which is another key thing. If you go up to Yuuka and treat her like a normal person, she will be nice to you as well. Distant, but very kind. Very wise, maybe even humble as well. It would probably be hard to grow closer to her though, nobody has actually done so after all. I really do think she's a loner, and that's probably the point I disagree with you on most. But she's probably ok with that. Either she simply got used to it, or she is very happy living a quiet life with her flowers and her naps.
Either way she's really complex and is far and away my favorite.