So angled body as a whole is good, but bum sticking out is bad? When you say angled body, are you referring to the type of posture in Demetrio's video? If that posture is a good thing, what advantages does it offer? (this is a serious question, not a challenge)
No worries Robin, and no, I was not referring to the video (to be honest, I hadn't actually watched it).
I was specifically commenting on Demetrio's post about the "Donald Duck" posture, which if I understood correctly, referred to Chris Hein's post about the "back hip sticking out" and leaning back into the hip. It would appear that Saito sensei considered this incorrect, as do other prominent teachers.
By angling the body as a whole, I meant moving it while keeping it connected. So my feeling is that within reason, we can tilt and manoeuvre the body however we like according to certain ingrained principles, of which one is not breaking connections. This includes the area around the lower back.
As for the posture etc in Demetrio's video link... I've never trained with Hitohira Sensei, but I'm not sure if some parts are representational of his normal teaching. I'd extend that to the photo Chris Hein posted, since the instructor highlighted is a prominent student of Saito Sensei, whom I've heard give salient advice on posture.