“I personally feel like Adwaita has been the pinnacle of Linux design and that the Gnome design guidelines are absolutely great.”
In libadwaita, headerbar buttons look exactly like the window title. The only things that still look clickable are the window controls. Flat design is a fashion, and the people it hurts are the ones who aren’t power users. GNOME spent years telling distros not to theme its apps. Now it themes everyone’s apps and shuts down anyone who complains.