It's hard to dispute a coverup when there are no facts to dispute, just what-if opinions.
On the other hand the investigative teams are like research teams. The members are not of all one mind. They compete to be heard. If you think that they can be silenced or kept away from data you are kidding yourself.
Even within tight organizations leaks will eventually occur if there is anything to be leaked. In the types of accident investigations being discussed here, there are just too many eyes and experts (including internet boards) to hide anything from.
In some of the examples discussed above I hear the same old claims which have been long ago discarded by the experts. So all that is new in this thread is the latest AF accident and patience should reveal something before calling it a coverup.