I dealt at a very low level with Boeing in the late 70's early 80's and later on more senior levels with GE, Hamiliton, Airesearch, etc. etc.
My impression from those years was that Boeing had a much better management style than McDonnell Douglas and listened closely to their customers. McD, on the other hand, always said "screw you, what would you know? We designed the DC3".
I also learned from McKinsey's that successful companies focussed on one business and one business only.
McDonnel Douglas screwed up its commercial aircraft division and was eventually taken over by Boeing.... Then Boeings leadership was taken over by the management of McDonnell Douglas! The same goons who screwed up that company! Then they moved headquarters out of Seattle and to St Louis!
Furthermore, while partnerships are all the rage, I don't think McDonnell Douglas ever ran a successful one. Boeing had, but I guess their Seattle based middle management weren't listened to.
My take on events - this was a predictable cluster****.