Writing proper documentation is definitely needed, but I have some strong concerns about the way users are supposed to setup MainUI. Some of the fundamentals are not quite right I believe.
As a release which is focussed on improving usability, OH3 failed in my opinion. Of course design posibilities have been greatly extended (which was definitely neccessary and the right move), but at the same time it is really hard (even for long-term OH users) to create a properly designed and working pages (beyond just adding a few widgets).
Many Users right away (have to) start looking for “how to’s”, secret hacks and workarounds and code snippets in the forum from people who have found ways to achieve certain layouts (partly by reverse-engineering OH). Thats’s exactly the same situation what most people were complaining about with OH2.