These numbers are based on daily statistics. Their astronomical proportions clearly reflect what an impact our individual Internet use can have when added to the impact of all the other indivual Internet users throughout the world.
Dark Mode can indeed reduce the display power draw by up to 58.5% at full brightness for the set of popular Android apps that we tested! In terms of whole phone battery drain reduction, that translates into 5.6% to 44.7% savings at full brightness and 1.8% to 23.5% savings at 38% brightness.
I know the numbers can be enormous and that is exactly why small steps matter. We're approx. 4 billion Internet users. If everybody takes the right decisions, we can have an impact and, apparently you took the good decisions.