So you have more than one cameras (enabled) in a scene … which one does the Unity Player choose to show as the main view?
How does the Camera.main command tie to this?
The MainCamera tag works perfectly fine. Note that it has nothing to do with “which one does the Unity Player choose to show as the main view”. Tags don’t “do” anything, they are just tags. What you do with the tags is up to you. Camera.main does exactly what the docs say it does: “The first enabled camera tagged “MainCamera” (Read Only).” e.g.:
// Disables the main camera
Camera.main.enabled = false;
If you have more than one camera tagged MainCamera, then which one it picks is undefined. So you really shouldn’t ever have more than one camera tagged MainCamera if you’re going to use Camera.main.