I think you’re measuring the wrong thing. Most email apps (and I sure hope the app in question is in this category) make the from, to, and subject lines part of the scrollable content region. In the example in question, I doubt they removed it — they scrolled it off the screen.

Amusingly, whoever made the blog post or perhaps the slide with the “4x faster” star seems to have doubled down on not caring about space allocated to content - the “4x faster” star also obscures the content!