I'm probably way out of the loop, but it seems weird to use a native look GUI library and then - if you're not using wxGTK - shoehorn in a text renderer from a different GUI library. What's the deal here?
I think I understand your point. Using GTK (and Pango Cairo) on Windows, by telling wxWidgets to use internally GTK seems duplicating window managers.
It's just a matter of taste. GTK in Windows does call Windows API to do windowing. But some users like the GTK-way for windows, menus, and other controls instead of the native Windows-way, and wxWidgets provides this feature (in addition, of course, of the native usage, keeping native look&feel).
Anyhow, GTK on Linux calls internaly X11 or Wayland for handling windows and menus. Do you also call this "duplicating"?