I mean, use it responsibly. Of course people won't, it's the internet, but a skilled designer may use it to highlight a word or an accent to draw your eye. It can be tricky in dense interfaces to draw focus to something (little tooltips or big buttons aren't the best answers). This is just another tool in the toolbox.
We haven't had dense interfaces for decades at this point.
Still, even with the best intent what you suggest is still annoying. Okay, you got my attention, i now know what you wanted me to know. Are you going to nag me for all eternity?
It’s bad because it dims the entire display. You’re assuming your app is more important than whatever else might be displayed. It can also take a bit for the os to go back to the sdr state. I’ve had a few cases where safari gets stuck in hdr mode and won’t revert u til I force closed.