Thing is, you people worked for years only on back-end stuff. You seem to know nothing about usability of user-facing parts (as evident by Weston's crappy usability). If KDE, Gnome, and Ubuntu applications got totally different title bars (in Ubuntu's case even with window buttons on the left side) because they're practically hardcoded because of CSD, it would hurt usability a lot more than stupid jagged pixel lines and those handful of people who resize Inkspace windows all the time.
At least in GTK and Qt CSD are optional. If you want to live in a usability nightmare, have fun there. I don't and that's why I'll turn CSD off and let KWin5 handle the window borders.
KWin has a good track record with performance and usability ever since Martin and Thomas took over main KWin development.