I have to ask what you are basing your opinions on if not for the AdSense reports you personally have access to?
Like I said go to any thread on this forum and any area and you will always find more people chiming in if someone starts a post with something wrong with their site(s). Why is this? Misery loves company (and I've shared mine at times too). If others post how they are doing great it only serves to p*ss people off and frustrate those that are not doing well even more.
With all the channel tools available I am not sure why anyone wouldn't be able to pin down what is exactly going wrong... was this page/section of the site bringing in $0.75 a click and now bringing in 15 cents etc.