Some types of application I prefer light, some dark. But the premise is wrong:
Saves your battery
Only if you're using OLED, which most people aren't, and by very little. You could save more battery by using a low-power mode when you don't need all the bells and whistles.
That doesn't sound right at all to me.
Majority of Internet traffic is on mobile, mobile devices far outnumber desktops, non-OLED phones are pretty rare
I’d argue light theme saves battery (for non-OLED displays), because then you don’t need to up the brightness so much. It’s the backlight that drains most battery, and if you use dark mode you tend to up the brightness to see anything.