What do you mean by "down hill"? Boeing has developed incredible technologies since the MD merger. They have been profitable w/ these technologies. You make a claim they were going down hill, what do you mean?
I have a number of family members that work for Boeing, that have been in executive management, engineering and research. None of them ever mentioned MD as being the beginning of a decline.
All of them tell a different story. The problems began with James McNerney. Harry Stonecipher came from MD, and was one of the best CEO's to ever touch that company. The 787 wouldn't have been a thing if it were not for McNerney.
If you make a claim, back it up.