Yes, not all readers will follow everything but my post is true and studying it will clear things up. However the movie will resit any attempted clarification.
You're right about phones and tablets, but fixed screens are rigidly landscape, hmmm.
I've found plenty of paintings etc that follow my portrait formula without being portraits. For example Van Gogh's various sunflowers paintings, the blossoms in the upper half and the less interesting vase in the lower half.
I don't pretend this article is a complete manual of composition.
By all means check out Winston, he's the master. Yes, you can find most of my rules elsewhere. But people don't know them. My student didn't. And my guess he picked up his bad habits listening to bad talks by clueless people. So these principles bear repeating.
You're right, writing stretch text with current HTML authoring tools is not practical. My MMP system was practical but the MMP server side software was a challenge to implement and now it's gone. But it will rise again!