I'm currently checking out Infragistics but I noticed you don't have support for ChromeWindow (or styling a normal WPF window)?
In your samples you just set the WindowStyle to none and then recreate all buttons. Is it correct that you don't have any support for window styling and leave it to us to do that?
I recommend using our xamRibbonWindow to style your application. You can read more about the xamRibbonWindow here: https://www.infragistics.com/help/wpf/xamribbon-ribbon-window
Please let me know if this component fits your needs, or if you have any specific questions regarding styling with xamRibbonWindow.