Thanks for the detailed feedback. However, most of the things you mention are documented on MDN, and you even link to some of them. The information that needs to be permanently available should be on MDN, I agree. I also agree that our documentation is fairly difficult to navigate, particularly for add-on development.
One of the benefits of having a well-defined API like WebExtensions is that it can be more easily documented. We will phase out the documentation for overlay and SDK add-ons as those become less important (this will take a couple of years), and the WebExtensions docs will hopefully be better organized.
We won’t stop blogging about these things, however. There are people who follow our posts but don’t read MDN regularly. Same goes with this forum, IRC, lists, etc. We have a very diverse audience with different entry points and preferences, and redundancy does more good than harm IMO.