The problem most designers and some devs do not seem to understand is that content creation in CMSs is already invented and pretty much standardised.

It is just like with the wheel. That has been invented several thousands of years ago and anyone who tried to reinvent it, has failed. The wheel is still round. So no matter how fancy UI you develop, people will just want to type letters and use images/videos/sound for illustration. In reality they just simply do not need all the hassle with too complicated technologies for so easy things. And by the way, those who create content, simply do not want a really fancy design as it would just distract your mind from the actual content they wanted to share. If you are hungry for design and eyecatching art, you should rather go to an art gallery, paginate picture books, paint pictures, etc.