I completely agree with your nice post RE quality, etc on various cars as I have also owned American, Japanese, and Mercedes in my life. My experience mirrors yours.
The way to improve quality is to recognize that there are imperfections on the cars and improve them. Denying out right is not the solution. Sorry I have to go back to the MAS one more time as a 14-year Mercedes-Benz Factory Tech posted today in
C36 stumbing/hesitation on acceleration
He said: "I think you having problems with the AirMass meter. I change at least 5-6 weekly on benz".
I think you have enough quotes from Mercedes-Benz mechnics and hope I have convinced you that Mercedes_benz HAVE PROBLEMS WITH THE DESIGN LOCATION OF THE MAS regardless if MBUSA will say it.
Now, if MBUSA recognizes that is a problem, it will find a way to improve it. Arrogantly denying it won't improve the quality. Recognizing behind the door and then improving it will alienate good customers.
Regarding easy to work on. Someone, please check the flat rate on a M103 or M104 water pump. Then check to see if there is another car or manufacture that requires the same amount of flat rate to replace a water pump. Or better yet, check the number of hours to replace a W140 condenser. MBUSA will laugh to the bank.
Mercedes-Bens are good cars. They are not the most trouble-free, they are not the best handling, they are not the most-economical. But they are a good compromise. They age well, their suspension is well designed and will last a long time if people throw money into that pit.
Again I will never blindly say Mercedes-Benz is the best on this and that. In terms of quality control and custom satisfaction, they have a lot to learn from the Japanese makers. Unfortunately, they will never learn or there will never be a need to learn unless forced upon. It took MBUSA 10 years to recognize their problem with the trap oxidizer and a lot of pressure from the EPA for them to "recall" that.