> This is “an obvious conclusion” which feels like it does not even need any justification. Sadly practice does not support it. MacOS Classic, Windows and other systems used this approach - and all of them had much better consistency then what we have in X world.
I claim that's incorrect statement. Window decorations were never issue for me on Linux. They are always consistent. Exactly because there is a single process handling them.
Besides consistency, because window manager draws decorations, I can easily configure different decorations (or lack of decorations) for different windows.