In the end the WYSIWYG would produce an XML file that you can put under version control. All depends on the UI of the thing your are building, if what you are building only needs to be functional and nobody cares about the UI (that is always the case of internal use software, that needs to have a good UX but who cares if it has the Windows 95 style controls, like machine HMIs, ERP software, etc.) WYSIWYG (like Visual Studio) are good to write things fast and typically with a consistent layout. I mean, most companies are not building a videogame, and most people are still fine using things like AS/400, so...