Why not the XR? You get a slightly smaller 7plus with taller screen and all of the features of XS bar the second camera and 3D Touch which both provide limited added value. On top of that you will have better battery as well.
The problem is that the taller screen is skinnier. And the width is most often the limiting size. For example, if you're watching a movie, a 16:9 image is limited by the width of the phone. So a skinnier screen means a smaller movie. Same for viewing photos. Basically most tasks result in a smaller viewing experience.
The taller screen really only buys you a better experience for reading long text (websites, ebooks, etc).
The only benefits to the Max over the XR are:
- even harder to see pixels (not that you'd notice them on the XR)
- 3d touch
- camera
Notably, it lacks an OLED display, perhaps (to me anyway) the best feature of the X.