I severely doubt that I could ever be comfortable with 10% of my screen getting much brighter than the value I set as max brightness.

But say you're right. Now you've achieved images looking completely out of place. You've achieved making the surrounding GUI look grey instead of white. And the screen looks broken when it suddenly dims after switching tabs away from one with an HDR video. What's the point? Even ignoring the painful aspects (which is a big thing to ignore, since my laptop currently physically hurts me at night with no setting to make it not hurt me, which I don't appreciate), you're just making the experience of browsing the web worse. Why?