I don't know why this manga is 6.5, sure the flash-back seems long, but it's just because of the time between the release of new chapters. I like how the author takes enough time to develop the character of Yuu's ex-gf and doesn't just say that they banged and got together but no one knows why. Otherwise it would just be another generic romance, where the whole plot is just both parties not wanting to confess to the other and the only turn of events is one making a mistake and revealing their feelings to the other.
I'm torn. I do
respect that the author cares enough to try and develop this relationship, to make it meaningful if only to inflict maximum possible pain. I don't like basically anything else about it. It comes completely out of left field, wrenches the plot away from the parts I was enjoying, and the whole twist itself has been such a
fundamental tone alteration that I can't possibly enjoy it the same way I was beforehand. It's basically a whole different manga, and it's hard not to feel like the original has been abandoned. The heroine's antics were my favorite part, and now not only is she MiA, but the moment she comes back is just going to be depressing. I can't say I'm in suspense.
I don't really think a 6.5 is warranted either, at least not yet. But I think it speaks to peoples' feelings more than an objective metric of quality; Something the author was clearly planning from the start still feels like it has stained the manga a bad color. A twist should draw you deeper into a world, not shock you out of it.
Like, imagine if you read Berserk up to the Eclipse, and then out of nowhere Miura shuffled Guts offscreen and suddenly started telling a harem comedy. Either you enjoy the first part only for it to change into something you don't, or you like the second part because you didn't really get invested in the first. It's a lose:lose. Sure, some people will appreciate the whole, but many (myself included) will prefer a side. It's a betrayal of expectations, plain and simple.
I don't know how they salvage this. Maybe there's some incredible master plan, but if I come back in a year and see a Tragedy tag, I won't be surprised. The current state of the main heroine hurts my heart. If the ending drops and I see that it's a happy one, then maybe I'll sit through the drama. I can weather a painful journey if I know the destination is good, but I'm not looking for a new twist of the knife every couple weeks.