Welcome to NPN David. This is a great first post, and it has sparked some very interesting discussion about what makes image have more impact. I agree with many of the comments made here, it has been an interesting discussion of creative possibilities.
My thought on this is that your comment on verticals is very dependent on the critical elements that are in a given image. In the case of this shot, I would agree with you, but that will not always be the case, it is image dependent. To me the choice of vertical vs. horizontal mainly depends on whether the image has stronger vertical or horizontal lines/ compositional elements. To me the most interesting elements in this image are the rock cliffs and the way the right side rock frames the background waterfall. To me the reflection is secondary, and not as interesting. Thus i like the rework done by @Han_Schutten. This image has both strong horizontal elements (the rock cliffs), and it has some interesting vertical elements (the trees). This is a case where Han’s squarish crop works well because it emphasizes both vertical and horizontal. In many images the main subject is clearly vertical or horizontal, and you should use the importance of the subject to dictate vertical vs. horizontal.
For example see this recent post by @Jimmy_Arcade, these trees are perfect for a vertical.