WYSIWYG editors that are not based on the structure of html, instead having an arbitrary drag&drop building procedure without providing access to css and hiding the DOM structure to make things “easy” and “user-friendly” will end up severely limited. Webflow basically forces the user to understand the core principles, yielding a steeper learning curve and a nice introduction to the box-model completely without code!
In terms of web apps, webflow can be useful for prototyping layouts quick and painless. The exported code however (while being quite decent, not like most generators) can get painful to clean for use inside frameworks! Especially if you create animations and transitions inside webflow, they will get attributes and classes from WF’s render engine and you’ll need to import the webflow.js file.
The css and js from WF can also be messy, if you use lots of combined classes!
If you only create layouts, no excessive styling and object-manipulations WF can be a fast and nice way to reduce hand-writing html.