Just adding some quick feedback:
As I've been playing around with the beta, I also kept thinking the same thing as I rarely change my guide from its setting (favorites) and have inadvertently changed it a few times while navigating back over to the left menu bar. The devs might have already considered this but two ideas came to mind: these guide categories could be moved to the top of the screen, which would then match the layout of the "On Now" section. Or maybe they could be put into a drop down menu like they are on the FireTV client. It's a good amount of space on the screen it could free up.
But otherwise lovin' the beta so far!