well, why don't you bring your physics and human anatomy arguing-from-first-principles over to wikipedia and let's see how long your changes last on that camera page :) good luck!

https://en.wikipedia.org/wiki/Single-lens_reflex_camera

opening paragraph

"In photography, a single-lens reflex camera (SLR) is a type of camera that uses a mirror and prism system to allow photographers to view through the lens and see exactly what will be captured... SLR technology played a crucial role in the evolution of modern photography...the rise of mirrorless cameras in the 2010s has led to a decline in SLR use and production. With twin lens reflex and rangefinder cameras, the viewed image could be significantly different from the final image."

what you see through the viewfinder is what the camera will take a picture of; you can change lenses so it is not always neutral. but if the zoom of the lens it neutral, what you will see through the viewfinder is neutral, and that occurs at 50mm for a 35mm camera