Outch, 30% is indeed a very bad default. 😵
On the bright side, this new feature (as far as I could read the MRs) can also control the brightness of display tablets, especially those without monitor buttons or OSD menu.
The previous method was via command line and wasn't user friendly, I wrote about it here: https://www.davidrevoy.com/article710/cintiqs-on-gnu-linux-how-to-setup-brightness-contrast-and-more