Nah, Yuna is straight up the worst character I've ever seen in any yuri series. Dumbest bitch ever, I swear she deserves nothing good happening to her in her entire life.
You clearly haven't read much, even in this series are 1 maybe even 2 characters who are way worse, but if you mean MC, even than she isn't the dumbest by far.
Yu-Na tries to protect Min-Ji, the way she does it is very dumb, that's right and not talking to her after coming out a few chapters ago also, but the good intention is still there, and it is for the others sake what at least gives her some points. I don't want to say she is a good and nice character but not so worse, that she deserves only sorrow.
Hye Ra on the other hand for example does everything just for her own sake and entertainment and when something doesn't work like she wants she immediately tries to destroy it.