Hmm. I'm skeptical, because my teacher is always warning me against the tension that comes from creating a bend at the wrist like that. But there's no harm in experimenting a little. I'll see if it helps. Thanks.
So I was correct in assuming the hand and forearm were aligned. There's no harm in bending at the wrist at all. Your fingers will naturally straighten as you bend the hand lower.
I really think you got lost in the context. That painting is an illustration of why having high wrists is not wrong, nor will it create tension. As well, since my solution to the difficulty of the broken octaves was to raise the wrists, I thought it was apt.And did you know, based on the OPs descriptions of his trouble, how he actually played the broken octaves? No, you didn't.
Why not practice scales in broken octaves in all key signatures? That should sort you out pretty fast! I recommend you do not consciously raise the wrist for this type of passage, although you will encounter different schools of thought on this subject.
What frustrates me is that I already do practice broken octave scales in all keys, and it hasn't sorted me out.
Perhaps you haven't been practicing them very effectively, then! Have you tried practicing the passage without the broken octave, but instead playing only the bass note of the broken octave OR the top note?
I like the advice about working on the arch, and I'll try to do that without ending up with a high, tense wrist.
You can't have the arch without the high wrist. You'll notice that simply holding the wrist higher will result in far less muscle tension in the fingers and you'll have to balance the angle of the wrist with the attack.