Again, you are getting offended. Not once did I suggest editor implementors are clueless. They're likely some of the best and sharpest developers out there. Please, as I mentioned earlier, take this project with a grain of salt.
By "fallen behind" I meant still making the assumption that many users are still using outdated browsers. This is not the case anymore, especially in the last year. And because of this fact, many WYSIWYG editors might be implementing a lot of cross-platform bloat that just isn't necessary any more. Rather than raging, perhaps browse through the ProseMirror source and see what you can remove as "obsolete" code.
ProseMirror was started 2 years ago, initially only targeted evergreen browser, and has recently grudgingly added support for IE11 because customers asked for it. But yeah, I guess for some parts of some of the older projects this may apply.
By "fallen behind" I meant still making the assumption that many users are still using outdated browsers. This is not the case anymore, especially in the last year. And because of this fact, many WYSIWYG editors might be implementing a lot of cross-platform bloat that just isn't necessary any more. Rather than raging, perhaps browse through the ProseMirror source and see what you can remove as "obsolete" code.