I don't believe this is a proven. The amount of code being run to cache objects, create and destroy objects, try not to create and destroy objects, marshal data into and out of GUI objects, manage and respond to events, etc. is easily 10x that of an ImGUI, maybe more. Many GUIs now a days are moved almost constantly. Pretty much all phone apps where the user scrolls through a feed of data. A static GUI doesn't need to be re-rendered in an ImGUI, only if something changes. Sure in some ideal test case the Retained mode GUI wins but I suspect it's far less clear what happens in the real world.