To make it clear, I would still use Linux with GNOME/libadwaita over Windows any day. Yes, some themes are ridiculous and will be a nightmare for any developer to work around. That said, I can’t help but be concerned about the coming demise of theming with the way GTK is going.
What first pushed me to start exploring Linux was when Windows 8 forced the Metro theme down our throats. My time with Linux would have started three years later if M$ had kept Windows 7 theming options - that’s how important a customizable, sensible theme is to me.
I’m glad that I don’t have to do that again since there are DE options that do insist on keeping theming alive.