I came from a 705 and miss so much about the navigation around the device.
You’re right, as far as I can tell the light button only affects the brightness of the screen, but not the back light. On the 705, the little joystick used to control the backlight. As above though, I just have the backlight set to on buried in the menus, and the brightness at 60 or 70%; the battery seems good enough for that for long day (can’t remember my last long day, mind).
My biggest gripe probably only affects me, but I wish the back and enter button were the other way around. I instinctively want to press the back button when I mean enter.
It’s a great little device apart from that mind.