I don't think that at the raw level there is that much of a difference. XCreateWindow() has mostly the same arguments as CreateWindowEx() except that the X11 AP

I don't think that at the raw level there is that much of a difference. XCreateWindow() has mostly the same arguments as CreateWindowEx() except that the X11 API only handles creating window and does not mash it together with upper layer concepts like event handling (lpClassName) and widget sets (hMenu). The X11 model is also easier to reason about because it is clear where the layer boundaries are and what is implemented in your process as opposed in the kernel/display server and what causes some kind of IPC (eg. what happens to lParam when you send message to window with WndProc implemented in different process?).