It's not the phone size, its the reach for my fingers. I can't reach the top left corner with my thumb on these larger screens and UI/UX people keep putting the hamburger for the navigation in that spot.
I understand it's not ideal, but I find it a valuable feature when I must operate one handed and sometimes struggle with the same issue.
I did also set up an accessibility feature where you can map a handful of actions to a double or triple tap on the back of the glass, and I mapped double-tap to trigger Reachability. But it's not super fast and overall a bit of a downgrade from the double capacitive TouchID tap on older models.